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<!-- Weave of 'Nonlocal Variables' generated by Inweb -->
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< ul class = "crumbs" > < li > < a href = "../index.html" > Home< / a > < / li > < li > < a href = "../compiler.html" > Inform7< / a > < / li > < li > < a href = "index.html" > knowledge< / a > < / li > < li > < a href = "index.html#2" > Chapter 2: Instances and Variables< / a > < / li > < li > < b > Nonlocal Variables< / b > < / li > < / ul > < / div >
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< p class = "purpose" > To manage variables whose scope is wider than the current rule.< / p >
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< p class = "commentary firstcommentary" > < a id = "SP1" class = "paragraph-anchor" > < / a > < b > § 1. < / b > The term "nonlocal variable" is less than elegant,< sup id = "fnref:1" > < a href = "#fn:1" rel = "footnote" > 1< / a > < / sup > but it expresses a basic
truth — that Inform, in contrast to C-like languages, has two different sorts
of variables:
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< / p >
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< ul class = "items" > < li > ● Local variables exist only in the current stack frame and therefore die
with it; assertions cannot declare their values; they are created with the
"let" phrase or similar, not by assertion sentences.
< / li > < li > ● Nonlocal variables, all of the others, exist across multiple stack frames,
and are longer-lived. We don't call these "global" because intermediate scopes
are also possible: rulebook, activity and action variables, for example, have
a limited scope and lifetime, but are nevertheless not local to any one rule.
These variables are created by assertion sentences.
< / li > < / ul >
< p class = "commentary" > These semantics are so different that it makes no compelling sense to try to
give them a common implementation inside the compiler; so, nonlocal variables
are handled below, but local variables have a different implementation at
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< a href = "../imperative-module/3-lv.html" class = "internal" > Local Variables (in imperative)< / a > .
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< / p >
< p class = "commentary" > A pragmatic, but questionable,< sup id = "fnref:2" > < a href = "#fn:2" rel = "footnote" > 2< / a > < / sup > implementation decision by Inform is that
names created as aliases for constant values are implemented as being variables
that happen not to vary.
< / p >
< p class = "commentary" > Nonlocal variables are stored in all kinds of ways at run-time. See
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< a href = "../runtime-module/5-vrb.html" class = "internal" > Variables (in runtime)< / a > for more.
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< / p >
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< ul class = "footnotetexts" > < li class = "footnote" id = "fn:1" > < p class = "inwebfootnote" > < sup id = "fnref:1" > < a href = "#fn:1" rel = "footnote" > 1< / a > < / sup > At one time the term used here was "quantity", which sounded philosophical
and was too vague.
< a href = "#fnref:1" title = "return to text" > ↩ < / a > < / p > < / li > < li class = "footnote" id = "fn:2" > < p class = "inwebfootnote" > < sup id = "fnref:2" > < a href = "#fn:2" rel = "footnote" > 2< / a > < / sup > Does it really make sense to regard named constants as being conceptually
closer to global variables than to literals such as < span class = "extract" > < span class = "extract-syntax" > true< / span > < / span > or < span class = "extract" > < span class = "extract-syntax" > false< / span > < / span > ?
< a href = "#fnref:2" title = "return to text" > ↩ < / a > < / p > < / li > < / ul >
< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > typedef< / span > < span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > {< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > wording< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > name< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > text of the name< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > kind< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv_kind< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > what kind of value it holds< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > shared_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > scope< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > where it exists, or < / span > < span class = "extract" > < span class = "extract-syntax" > NULL< / span > < / span > < span class = "comment-syntax" > for everywhere< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > inference_subject< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > as_subject< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > so that assertions can discuss it...< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > inference_subject< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > alias_subject< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > ...or perhaps the thing it aliases< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > constant_at_run_time< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > for instance, for "story title"< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > substitution_marker< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > to prevent infinite regress when substituting< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > var_is_bibliographic< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > one of the bibliographic constants set at the end< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > var_is_allowed_to_be_zero< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > for an empty enumerated kind, despite non-safety< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > variable_compilation_data< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > compilation_data< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > parse_node< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv_created_at< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > sentence creating the variable< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > struct< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > wording< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > var_documentation_symbol< / span > < span class = "plain-syntax" > ; < / span > < span class = "comment-syntax" > reference to manual, if any< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > CLASS_DEFINITION< / span >
< span class = "plain-syntax" > } < / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > ;< / span >
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< / pre >
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< ul class = "endnotetexts" > < li > The structure nonlocal_variable is accessed in 2/ins, 3/prp, 3/vp, 3/spr, 3/msr, 4/vs, 5/pi, 5/tmw, 5/tnt and here.< / li > < / ul >
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< p class = "commentary firstcommentary" > < a id = "SP2" class = "paragraph-anchor" > < / a > < b > § 2. < / b > We can create a new variable provided we give its name, kind and scope.
When the scope isn't global, the variable is said to be "stacked", which is a
reference to how it's stored at run-time.
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< / p >
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< p class = "commentary" > Note that we only register the name of the variable as a proper noun if it's
global and will live forever, because nouns are both of those things. Anyone
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creating a shared variable will have to make their own arrangements to parse
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the names of them.
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "function-syntax" > NonlocalVariables::new_global< / span > < button class = "popup" onclick = "togglePopup('usagePopup1')" > < span class = "comment-syntax" > ?< / span > < span class = "popuptext" id = "usagePopup1" > Usage of < span class = "code-font" > < span class = "function-syntax" > NonlocalVariables::new_global< / span > < / span > :< br / > Assert Propositions - < a href = "1-ap.html#SP6_5_2" > § 6.5.2< / a > < / span > < / button > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > wording< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > kind< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > ) {< / span >
< span class = "plain-syntax" > < / span > < span class = "constant-syntax" > PROTECTED_MODEL_PROCEDURE< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > = < / span > < a href = "2-nv.html#SP4" class = "function-link" > < span class = "function-syntax" > NonlocalVariables::new< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Wordings::nonempty< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > name< / span > < span class = "plain-syntax" > )) {< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Nouns::new_proper_noun< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > name< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > NEUTER_GENDER< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > ADD_TO_LEXICON_NTOPT< / span > < span class = "plain-syntax" > ,< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > VARIABLE_MC< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > Lvalues::new_actual_NONLOCAL_VARIABLE< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ),< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Task::language_of_syntax< / span > < span class = "plain-syntax" > ());< / span >
< span class = "plain-syntax" > }< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP3" class = "paragraph-anchor" > < / a > < b > § 3. < / b > The following then parses for those nouns, and note that it therefore can
only match globals, since variables of lesser scope are not in the lexicon.
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "function-syntax" > NonlocalVariables::parse_global< / span > < button class = "popup" onclick = "togglePopup('usagePopup2')" > < span class = "comment-syntax" > ?< / span > < span class = "popuptext" id = "usagePopup2" > Usage of < span class = "code-font" > < span class = "function-syntax" > NonlocalVariables::parse_global< / span > < / span > :< br / > < a href = "2-nv.html#SP6" > § 6< / a > < / span > < / button > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > wording< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > Articles::remove_the< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "function-syntax" > < s-global-variable> < / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > )) {< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > parse_node< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > val< / span > < span class = "plain-syntax" > = < / span > < span class = "function-syntax" > < < rp> > < / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Node::get_constant_nonlocal_variable< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > val< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > }< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP4" class = "paragraph-anchor" > < / a > < b > § 4. < / b > We record the one most recently made:
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > latest_nonlocal_variable< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ;< / span >
< span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "function-syntax" > NonlocalVariables::get_latest< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > void< / span > < span class = "plain-syntax" > ) {< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > latest_nonlocal_variable< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
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< span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "function-syntax" > NonlocalVariables::new< / span > < button class = "popup" onclick = "togglePopup('usagePopup3')" > < span class = "comment-syntax" > ?< / span > < span class = "popuptext" id = "usagePopup3" > Usage of < span class = "code-font" > < span class = "function-syntax" > NonlocalVariables::new< / span > < / span > :< br / > < a href = "2-nv.html#SP2" > § 2< / a > < / span > < / button > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > wording< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > kind< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > shared_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > shv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > == < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ) < / span > < span class = "identifier-syntax" > internal_error< / span > < span class = "plain-syntax" > (< / span > < span class = "string-syntax" > "created variable without kind"< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Kinds::Behaviour::definite< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > ) == < / span > < span class = "identifier-syntax" > FALSE< / span > < span class = "plain-syntax" > )< / span >
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< span class = "plain-syntax" > < / span > < span class = "named-paragraph-container code-font" > < a href = "2-nv.html#SP4_1" class = "named-paragraph-link" > < span class = "named-paragraph" > Issue problem message for an indefinite variable< / span > < span class = "named-paragraph-number" > 4.1< / span > < / a > < / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > CREATE< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > latest_nonlocal_variable< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > var_documentation_symbol< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > Index::DocReferences::position_of_symbol< / span > < span class = "plain-syntax" > (& < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > name< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > nlv_created_at< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > current_sentence< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > nlv_kind< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > alias_subject< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > constant_at_run_time< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > FALSE< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > var_is_allowed_to_be_zero< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > FALSE< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > scope< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > shv< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > substitution_marker< / span > < span class = "plain-syntax" > = < / span > < span class = "constant-syntax" > 0< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > as_subject< / span > < span class = "plain-syntax" > = < / span > < a href = "4-vs.html#SP1" class = "function-link" > < span class = "function-syntax" > VariableSubjects::new< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > compilation_data< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > RTVariables::new_compilation_data< / span > < span class = "plain-syntax" > ();< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > RTTemporaryVariables::new_variable_notify< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > PluginCalls::new_variable_notify< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > LOGIF< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > VARIABLE_CREATIONS< / span > < span class = "plain-syntax" > , < / span > < span class = "string-syntax" > "Created nonlocal variable: $Z\n"< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP4_1" class = "paragraph-anchor" > < / a > < b > § 4.1. < / b > < span class = "named-paragraph-container code-font" > < span class = "named-paragraph-defn" > Issue problem message for an indefinite variable< / span > < span class = "named-paragraph-number" > 4.1< / span > < / span > < span class = "comment-syntax" > =< / span >
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::quote_wording< / span > < span class = "plain-syntax" > (1, < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::quote_kind< / span > < span class = "plain-syntax" > (2, < / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > StandardProblems::handmade_problem< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Task::syntax_tree< / span > < span class = "plain-syntax" > (),< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > _p_< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > PM_IndefiniteVariable< / span > < span class = "plain-syntax" > ));< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::issue_problem_segment< / span > < span class = "plain-syntax" > (< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "I am unable to create the variable '%1', because its kind (%2) is too "< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "vague. I need to know exactly what kind of value goes into each "< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "variable: for instance, it's not enough to say 'L is a list of values "< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "that varies', because I don't know what the entries have to be - 'L "< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "is a list of numbers that varies' would be better."< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::issue_problem_end< / span > < span class = "plain-syntax" > ();< / span >
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< / pre >
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< ul class = "endnotetexts" > < li > This code is used in < a href = "2-nv.html#SP4" > § 4< / a > .< / li > < / ul >
< p class = "commentary firstcommentary" > < a id = "SP5" class = "paragraph-anchor" > < / a > < b > § 5. < / b > So much for creation; and here's how we log and write them:
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< / p >
< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > void< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::log< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < a href = "2-nv.html#SP5" class = "function-link" > < span class = "function-syntax" > NonlocalVariables::write< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > DL< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > }< / span >
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< span class = "reserved-syntax" > void< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::write< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > OUTPUT_STREAM< / span > < span class = "plain-syntax" > , < / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > == < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ) { < / span > < span class = "identifier-syntax" > WRITE< / span > < span class = "plain-syntax" > (< / span > < span class = "string-syntax" > "< null variable> "< / span > < span class = "plain-syntax" > ); < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > ; }< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > WRITE< / span > < span class = "plain-syntax" > (< / span > < span class = "string-syntax" > "'%W'(%s)"< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > name< / span > < span class = "plain-syntax" > , (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > constant_at_run_time< / span > < span class = "plain-syntax" > )?< / span > < span class = "string-syntax" > "const"< / span > < span class = "plain-syntax" > :< / span > < span class = "string-syntax" > "var"< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Kinds::Textual::write< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > OUT< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > nlv_kind< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP6" class = "paragraph-anchor" > < / a > < b > § 6. < / b > The author can demand with a "translates as" sentence that a given
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variable is equivalent to an Inter variable supplied in some kit:
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > void< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::translates< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > wording< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > parse_node< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > p2< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > = < / span > < a href = "2-nv.html#SP3" class = "function-link" > < span class = "function-syntax" > NonlocalVariables::parse_global< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > ((< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > == < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ) || (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > scope< / span > < span class = "plain-syntax" > )) {< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > LOG< / span > < span class = "plain-syntax" > (< / span > < span class = "string-syntax" > "Tried %W\n"< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > W< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > StandardProblems::sentence_problem< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Task::syntax_tree< / span > < span class = "plain-syntax" > (),< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > _p_< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > PM_NonQuantityTranslated< / span > < span class = "plain-syntax" > ),< / span >
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< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "this is not the name of a variable"< / span > < span class = "plain-syntax" > ,< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "or at any rate not one global in scope."< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > TEMPORARY_TEXT< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > name< / span > < span class = "plain-syntax" > )< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > WRITE_TO< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > name< / span > < span class = "plain-syntax" > , < / span > < span class = "string-syntax" > "%N"< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > Wordings::first_wn< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Node::get_text< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > p2< / span > < span class = "plain-syntax" > )));< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > RTVariables::identifier_translates< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > name< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > DISCARD_TEXT< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > name< / span > < span class = "plain-syntax" > )< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > LOGIF< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > VARIABLE_CREATIONS< / span > < span class = "plain-syntax" > ,< / span >
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< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "Translated variable: $Z as %N\n"< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ,< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Wordings::first_wn< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Node::get_text< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > p2< / span > < span class = "plain-syntax" > )));< / span >
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< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP7" class = "paragraph-anchor" > < / a > < b > § 7. < / b > Nonlocal variables are inference subjects in order that they can be given
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initial values by inference: see < a href = "4-vs.html" class = "internal" > Variable Subjects< / a > for more.
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > inference_subject< / span > < span class = "plain-syntax" > *< / span > < span class = "function-syntax" > NonlocalVariables::to_subject< / span > < button class = "popup" onclick = "togglePopup('usagePopup4')" > < span class = "comment-syntax" > ?< / span > < span class = "popuptext" id = "usagePopup4" > Usage of < span class = "code-font" > < span class = "function-syntax" > NonlocalVariables::to_subject< / span > < / span > :< br / > < a href = "2-nv.html#SP10" > § 10< / a > < br / > Variable Subjects - < a href = "4-vs.html#SP2" > § 2< / a > < / span > < / button > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > as_subject< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP8" class = "paragraph-anchor" > < / a > < b > § 8. < / b > Now for some basic properties:
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::is_global< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > scope< / span > < span class = "plain-syntax" > ) < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > FALSE< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > TRUE< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< span class = "identifier-syntax" > kind< / span > < span class = "plain-syntax" > *< / span > < span class = "function-syntax" > NonlocalVariables::kind< / span > < button class = "popup" onclick = "togglePopup('usagePopup5')" > < span class = "comment-syntax" > ?< / span > < span class = "popuptext" id = "usagePopup5" > Usage of < span class = "code-font" > < span class = "function-syntax" > NonlocalVariables::kind< / span > < / span > :< br / > Variable Subjects - < a href = "4-vs.html#SP3" > § 3< / a > < / span > < / button > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > == < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ) < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > nlv_kind< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< span class = "reserved-syntax" > void< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::allow_to_be_zero< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > var_is_allowed_to_be_zero< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > TRUE< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP9" class = "paragraph-anchor" > < / a > < b > § 9. < / b > The kind can in fact be changed after creation, though this never happens
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to variables declared in source text: it allows us to have a few globals which
are reused for different purposes and are typeless.
< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > void< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::set_kind< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > kind< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > == < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ) < / span > < span class = "identifier-syntax" > internal_error< / span > < span class = "plain-syntax" > (< / span > < span class = "string-syntax" > "set kind for null variable"< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > nlv_kind< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > K< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP10" class = "paragraph-anchor" > < / a > < b > § 10. < / b > This is a curiosity, used to force the textual contents of a bibliographic
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data variable (such as "story title") to be treated as text.
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "identifier-syntax" > wording< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::initial_value_as_plain_text< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > inference< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > inf< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > inference_subject< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > infs< / span > < span class = "plain-syntax" > = < / span > < a href = "2-nv.html#SP7" class = "function-link" > < span class = "function-syntax" > NonlocalVariables::to_subject< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > POSITIVE_KNOWLEDGE_LOOP< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > inf< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > infs< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > property_inf< / span > < span class = "plain-syntax" > )< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < a href = "5-pi.html#SP7" class = "function-link" > < span class = "function-syntax" > PropertyInferences::get_property< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > inf< / span > < span class = "plain-syntax" > ) == < / span > < span class = "identifier-syntax" > P_variable_initial_value< / span > < span class = "plain-syntax" > )< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Node::get_text< / span > < span class = "plain-syntax" > (< / span >
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< span class = "plain-syntax" > < / span > < a href = "5-pi.html#SP8" class = "function-link" > < span class = "function-syntax" > PropertyInferences::set_value_kind< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > inf< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > K_text< / span > < span class = "plain-syntax" > ));< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > EMPTY_WORDING< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP11" class = "paragraph-anchor" > < / a > < b > § 11. < / b > "Constant" means that no change is permitted at run-time; "initialisable"
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means that a value can be set by an assertion in the source text.
< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > void< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::make_constant< / span > < button class = "popup" onclick = "togglePopup('usagePopup6')" > < span class = "comment-syntax" > ?< / span > < span class = "popuptext" id = "usagePopup6" > Usage of < span class = "code-font" > < span class = "function-syntax" > NonlocalVariables::make_constant< / span > < / span > :< br / > Assert Propositions - < a href = "1-ap.html#SP6_5_2" > § 6.5.2< / a > < / span > < / button > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > , < / span > < span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > bib< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > == < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ) < / span > < span class = "identifier-syntax" > internal_error< / span > < span class = "plain-syntax" > (< / span > < span class = "string-syntax" > "no such var"< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > constant_at_run_time< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > TRUE< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > var_is_bibliographic< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > bib< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > RTVariables::make_initialisable< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > }< / span >
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< span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::is_constant< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > == < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ) < / span > < span class = "identifier-syntax" > internal_error< / span > < span class = "plain-syntax" > (< / span > < span class = "string-syntax" > "no such var"< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > constant_at_run_time< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
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< span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::must_be_constant< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > constant_at_run_time< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > StandardProblems::sentence_problem< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Task::syntax_tree< / span > < span class = "plain-syntax" > (),< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > _p_< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > PM_CantChangeConstants< / span > < span class = "plain-syntax" > ),< / span >
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< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "this is a name for a value which never changes during the story"< / span > < span class = "plain-syntax" > ,< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "so it can't be altered with 'now'."< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > TRUE< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > FALSE< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP12" class = "paragraph-anchor" > < / a > < b > § 12. < / b > Substitution is the down-side if handling constants as if they were variables.
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At some point, the constant has to be replaced by its value, and this is where.
Note that it's easy to imagine a chain of constants defined each as being
equal to the next, but that a cycle of those is illegal.
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< / p >
< pre class = "displayed-code all-displayed-code code-font" >
< span class = "reserved-syntax" > int< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > substitution_session_id< / span > < span class = "plain-syntax" > = < / span > < span class = "constant-syntax" > 0< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "identifier-syntax" > parse_node< / span > < span class = "plain-syntax" > *< / span > < span class = "function-syntax" > NonlocalVariables::substitute_constants< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > parse_node< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > spec< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > substitution_session_id< / span > < span class = "plain-syntax" > ++;< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > while< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > TRUE< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > Lvalues::get_nonlocal_variable_if_any< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > spec< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > ((< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) & & (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > constant_at_run_time< / span > < span class = "plain-syntax" > )) {< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > substitution_marker< / span > < span class = "plain-syntax" > == < / span > < span class = "identifier-syntax" > substitution_session_id< / span > < span class = "plain-syntax" > ) {< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::quote_source< / span > < span class = "plain-syntax" > (1, < / span > < span class = "identifier-syntax" > current_sentence< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::quote_wording< / span > < span class = "plain-syntax" > (2, < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > name< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::quote_kind< / span > < span class = "plain-syntax" > (3, < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > nlv_kind< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > StandardProblems::handmade_problem< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Task::syntax_tree< / span > < span class = "plain-syntax" > (),< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > _p_< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > PM_MeaningRecursive< / span > < span class = "plain-syntax" > ));< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::issue_problem_segment< / span > < span class = "plain-syntax" > (< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "The sentence %1 tells me that '%2', which should be %3 "< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "that varies, is to have an initial value which can't "< / span >
< span class = "plain-syntax" > < / span > < span class = "string-syntax" > "be worked out without going round in circles."< / span > < span class = "plain-syntax" > );< / span >
< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > Problems::issue_problem_end< / span > < span class = "plain-syntax" > ();< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > spec< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > Specifications::new_UNKNOWN< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Node::get_text< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > spec< / span > < span class = "plain-syntax" > ));< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > break< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > substitution_marker< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > substitution_session_id< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > parse_node< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > sspec< / span > < span class = "plain-syntax" > = < / span > < a href = "4-vs.html#SP2" class = "function-link" > < span class = "function-syntax" > VariableSubjects::get_initial_value< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > Node::is< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > sspec< / span > < span class = "plain-syntax" > , < / span > < span class = "identifier-syntax" > UNKNOWN_NT< / span > < span class = "plain-syntax" > ) == < / span > < span class = "identifier-syntax" > FALSE< / span > < span class = "plain-syntax" > ) { < / span > < span class = "identifier-syntax" > spec< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > sspec< / span > < span class = "plain-syntax" > ; < / span > < span class = "reserved-syntax" > continue< / span > < span class = "plain-syntax" > ; }< / span >
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< span class = "plain-syntax" > }< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > break< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > spec< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
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< / pre >
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< p class = "commentary firstcommentary" > < a id = "SP13" class = "paragraph-anchor" > < / a > < b > § 13. < / b > "Aliasing" is the ability to divert inferences about a variable to
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inferences about something else. Inform uses this for interactive fiction
projects with "the player"; authors tend to think "the player" is an instance
and they write assertions accordingly, but in fact it's a variable. Because
of this aliasing, however, an inference about "the player" is diverted to
become an inference about "yourself", the actual default player instance.
< / p >
< p class = "commentary" > At present this is the only use made of aliasing.
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< / p >
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< pre class = "displayed-code all-displayed-code code-font" >
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< span class = "reserved-syntax" > inference_subject< / span > < span class = "plain-syntax" > *< / span > < span class = "function-syntax" > NonlocalVariables::get_alias< / span > < button class = "popup" onclick = "togglePopup('usagePopup7')" > < span class = "comment-syntax" > ?< / span > < span class = "popuptext" id = "usagePopup7" > Usage of < span class = "code-font" > < span class = "function-syntax" > NonlocalVariables::get_alias< / span > < / span > :< br / > Assert Propositions - < a href = "1-ap.html#SP9" > § 9< / a > < / span > < / button > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > parse_node< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > val< / span > < span class = "plain-syntax" > = < / span > < a href = "4-vs.html#SP2" class = "function-link" > < span class = "function-syntax" > VariableSubjects::get_initial_value< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > inference_subject< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > vals< / span > < span class = "plain-syntax" > = < / span > < a href = "4-is.html#SP14" class = "function-link" > < span class = "function-syntax" > InferenceSubjects::from_specification< / span > < / a > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > val< / span > < span class = "plain-syntax" > );< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > if< / span > < span class = "plain-syntax" > (< / span > < span class = "identifier-syntax" > vals< / span > < span class = "plain-syntax" > ) < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > vals< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > alias_subject< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
< span class = "plain-syntax" > < / span > < span class = "reserved-syntax" > return< / span > < span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > NULL< / span > < span class = "plain-syntax" > ;< / span >
< span class = "plain-syntax" > }< / span >
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< span class = "reserved-syntax" > void< / span > < span class = "plain-syntax" > < / span > < span class = "function-syntax" > NonlocalVariables::set_alias< / span > < span class = "plain-syntax" > (< / span > < span class = "reserved-syntax" > nonlocal_variable< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > , < / span > < span class = "reserved-syntax" > inference_subject< / span > < span class = "plain-syntax" > *< / span > < span class = "identifier-syntax" > infs< / span > < span class = "plain-syntax" > ) {< / span >
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< span class = "plain-syntax" > < / span > < span class = "identifier-syntax" > nlv< / span > < span class = "plain-syntax" > -> < / span > < span class = "element-syntax" > alias_subject< / span > < span class = "plain-syntax" > = < / span > < span class = "identifier-syntax" > infs< / span > < span class = "plain-syntax" > ;< / span >
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< span class = "plain-syntax" > }< / span >
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< / pre >
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< nav role = "progress" > < div class = "progresscontainer" >
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< ul class = "progressbar" > < li class = "progressprev" > < a href = "2-oi.html" > ❮ < / a > < / li > < li class = "progresschapter" > < a href = "P-wtmd.html" > P< / a > < / li > < li class = "progresschapter" > < a href = "1-km.html" > 1< / a > < / li > < li class = "progresscurrentchapter" > 2< / li > < li class = "progresssection" > < a href = "2-ins.html" > ins< / a > < / li > < li class = "progresssection" > < a href = "2-iaa.html" > iaa< / a > < / li > < li class = "progresssection" > < a href = "2-pfi.html" > pfi< / a > < / li > < li class = "progresssection" > < a href = "2-oi.html" > oi< / a > < / li > < li class = "progresscurrent" > nv< / li > < li class = "progresschapter" > < a href = "3-prp.html" > 3< / a > < / li > < li class = "progresschapter" > < a href = "4-is.html" > 4< / a > < / li > < li class = "progresschapter" > < a href = "5-inf.html" > 5< / a > < / li > < li class = "progressnext" > < a href = "3-prp.html" > ❯ < / a > < / li > < / ul > < / div >
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< / nav > <!-- End of weave -->
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< / main >
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< / body >
< / html >
