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<!--Weave of 'Inform Primitives' generated by Inweb-->
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<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../compiler.html">Compiler Tools</a></li><li><a href="index.html">inter</a></li><li><a href="index.html#M">Manual</a></li><li><b>Inform Primitives</b></li></ul></div>
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<p class="purpose">The standard set of primitive invocations used within Inform.</p>
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<ul class="toc"><li><a href="M-ip.html#SP1">§1. Status</a></li><li><a href="M-ip.html#SP2">§2. Arithmetic</a></li><li><a href="M-ip.html#SP3">§3. Logical operators</a></li><li><a href="M-ip.html#SP4">§4. Bitwise operators</a></li><li><a href="M-ip.html#SP5">§5. Numerical comparison</a></li><li><a href="M-ip.html#SP6">§6. Sequential evaluation</a></li><li><a href="M-ip.html#SP7">§7. Random numbers</a></li><li><a href="M-ip.html#SP8">§8. Printing</a></li><li><a href="M-ip.html#SP9">§9. Stack access</a></li><li><a href="M-ip.html#SP10">§10. Accessing storage</a></li><li><a href="M-ip.html#SP11">§11. Indirect function calls</a></li><li><a href="M-ip.html#SP12">§12. Control flow</a></li><li><a href="M-ip.html#SP13">§13. Interactive fiction-only primitives</a></li></ul><hr class="tocbar">
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<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>§1. Status. </b>The Inter specification allows for any number of primitive invocations to
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be declared and used; none are built-in or required.
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</p>
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<p class="commentary">The Inform compiler, however, has a set of around 90 different primitives.
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The back end of the compiler can compile those into valid Inform 6 code;
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the front end of the compiler is guaranteed to declare and use only (a
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subset of) those 90. That gives the following set of primitives a
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kind of halfway status: though they are not part of the inter specification,
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for the time being they're the only game in town.
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</p>
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<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>§2. Arithmetic. </b>The following are standard integer arithmetic operations:
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !plus val val -> val</span></span>. 16 or 32-bit integer addition.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !minus val val -> val</span></span>. 16 or 32-bit integer subtraction.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !unaryminus val -> val</span></span>. Equivalent to performing <span class="extract"><span class="extract-syntax">0 - x</span></span>.
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</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !times val val -> val</span></span>. 16 or 32-bit integer multiplication.
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</li><li>(e) <span class="extract"><span class="extract-syntax">primitive !divide val val -> val</span></span>. 16 or 32-bit integer division.
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</li><li>(f) <span class="extract"><span class="extract-syntax">primitive !modulo val val -> val</span></span>. Remainder after such a division.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>§3. Logical operators. </b>In general, the value 0 is false, and all other values are true.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !not val -> val</span></span>. True if the value is false, and vice versa.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !and val val -> val</span></span>. True if both are true: doesn't evaluate the second if the first is false.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !or val val -> val</span></span>. True if either is true: doesn't evaluate the second if the first is true.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>§4. Bitwise operators. </b>These differ in that they do not "short circuit", and do not squash values
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down to just 0 or 1.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !bitwiseand val val -> val</span></span>.
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</li><li>(a) <span class="extract"><span class="extract-syntax">primitive !bitwiseor val val -> val</span></span>.
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</li><li>(a) <span class="extract"><span class="extract-syntax">primitive !bitwisenot val -> val</span></span>.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP5" class="paragraph-anchor"></a><b>§5. Numerical comparison. </b>These are comparisons of signed integers. (If Inform needs to compare unsigned
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integers, it calls a routine in the I6 template.)
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !eq val val -> val</span></span>.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !ne val val -> val</span></span>.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !gt val val -> val</span></span>.
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</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !ge val val -> val</span></span>.
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</li><li>(e) <span class="extract"><span class="extract-syntax">primitive !lt val val -> val</span></span>.
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</li><li>(f) <span class="extract"><span class="extract-syntax">primitive !le val val -> val</span></span>.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP6" class="paragraph-anchor"></a><b>§6. Sequential evaluation. </b>The reason for the existence of <span class="extract"><span class="extract-syntax">!ternarysequential</span></span> is that it's a convenient
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shorthand, and also that it helps the code generator with I6 generation,
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because I6 has problems with the syntax of complicated sequential evals.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !sequential val val -> val</span></span>. Evaluates the first, then the second
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value, producing that second value.
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</li><li>(a) <span class="extract"><span class="extract-syntax">primitive !ternarysequential val val val -> val</span></span>. Evaluates the first,
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then the second, then the third value, producing that third value.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP7" class="paragraph-anchor"></a><b>§7. Random numbers. </b>There is just one primitive for this:
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !random val -> val</span></span>. Produce a uniformly random integer in the range 0 up to <span class="extract"><span class="extract-syntax">val</span></span> minus 1.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP8" class="paragraph-anchor"></a><b>§8. Printing. </b>These print data of various kinds:
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !print val -> void</span></span>. Print text.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !printnumber val -> void</span></span>. Print a (signed) number in decimal.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !printchar val -> void</span></span>. Print a character value, from the ZSCII character set.
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</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !printaddress val -> void</span></span>. Print a dictionary word.
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</li><li>(e) <span class="extract"><span class="extract-syntax">primitive !printstring val -> void</span></span>. Print a packed string.
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</li></ul>
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<p class="commentary">While these correspond to standard I6 library functions, they should probably
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be removed from the set of primitives, but there are issues here to do with
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the Inform 6 "veneer":
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !printnlnumber val -> void</span></span>. Print number but in natural language.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !printname val -> void</span></span>. Print name of an object.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !printdef val -> void</span></span>. Print name of an object, preceded by definite article.
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</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !printcdef val -> void</span></span>. Print name of an object, preceded by capitalised definite article.
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</li><li>(e) <span class="extract"><span class="extract-syntax">primitive !printindef val -> void</span></span>. Print name of an object, preceded by indefinite article.
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</li><li>(f) <span class="extract"><span class="extract-syntax">primitive !printcindef val -> void</span></span>. Print name of an object, preceded by capitalised indefinite article.
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</li></ul>
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<p class="commentary">There are also primitive ways to change the visual style of text:
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !font val -> void</span></span>. Change to fixed-width font if value is 1, or regular if 0.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !stylebold void -> void</span></span>. Change to bold type.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !styleunderline void -> void</span></span>. Change to underlined type.
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</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !styleroman void -> void</span></span>. Change to roman (i.e., not bold, not underlined) type.
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</li></ul>
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<p class="commentary">Lastly, a primitive for a rum feature of Inform 6 allowing for the display of
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"box quotations" on screen:
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !box val -> void</span></span>.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP9" class="paragraph-anchor"></a><b>§9. Stack access. </b>The stack is not directly accessible anywhere in memory, so the only access
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is via the following.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !push val -> void</span></span>. Push value onto the stack.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !pull ref -> void</span></span>. Pull value from the stack and write it into
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the storage referred to. Values on the stack have unchecked kinds: it's up to
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the author not to pull an inappropriate value.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP10" class="paragraph-anchor"></a><b>§10. Accessing storage. </b>Here the <span class="extract"><span class="extract-syntax">ref</span></span> term is a refernce to a piece of storage: a property of an
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instance, or a global variable, or an entry in memory, for example.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !store ref val -> val</span></span>. Put the value in <span class="extract"><span class="extract-syntax">ref</span></span>.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !setbit ref val -> void</span></span>. Set bits in the mask <span class="extract"><span class="extract-syntax">val</span></span> in <span class="extract"><span class="extract-syntax">ref</span></span>.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !clearbit ref val -> void</span></span>. Clear bits in the mask <span class="extract"><span class="extract-syntax">val</span></span> in <span class="extract"><span class="extract-syntax">ref</span></span>.
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</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !postincrement ref -> val</span></span>. Performs the equivalent of <span class="extract"><span class="extract-syntax">ref++</span></span>.
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</li><li>(e) <span class="extract"><span class="extract-syntax">primitive !preincrement ref -> val</span></span>. Performs the equivalent of <span class="extract"><span class="extract-syntax">++ref</span></span>.
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</li><li>(f) <span class="extract"><span class="extract-syntax">primitive !postdecrement ref -> val</span></span>. Performs the equivalent of <span class="extract"><span class="extract-syntax">ref--</span></span>.
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</li><li>(g) <span class="extract"><span class="extract-syntax">primitive !predecrement ref -> val</span></span>. Performs the equivalent of <span class="extract"><span class="extract-syntax">--ref</span></span>.
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</li></ul>
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<p class="commentary">Memory can be read with the following. The first value is the address of
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the array; the second is an offset, that is, with 0 being the first entry,
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1 the second, and so on. "Word" in this context means either an <span class="extract"><span class="extract-syntax">int16</span></span> or
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an <span class="extract"><span class="extract-syntax">int32</span></span>, depending on what virtual machine are compiling to.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !lookup val val -> val</span></span>. Find word at this word offset.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !lookupbyte val val -> val</span></span>. Find byte at this byte offset.
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</li></ul>
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<p class="commentary">Those however only read from array entries. To write to array entries, we
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need to use <span class="extract"><span class="extract-syntax">!store</span></span> or similar (see above); but to do that, we need a
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reference for the memory cell. We do that with:
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !lookupref val val -> ref</span></span>.
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</li></ul>
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<p class="commentary">(There is at present no equivalent for byte arrays.)
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</p>
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<p class="commentary firstcommentary"><a id="SP11" class="paragraph-anchor"></a><b>§11. Indirect function calls. </b>Invocations of functions can only be made with <span class="extract"><span class="extract-syntax">inv</span></span> when the function is
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specified as a constant, and when its signature is therefore known. If
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we need to call "whatever function this variable refers to", we have to
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use one of the following. They differ only in their signatures. The
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first value is the function address, and subsequent ones are arguments.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !indirect0v val -> void</span></span>.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !indirect1v val val -> void</span></span>.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !indirect2v val val val -> void</span></span>.
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</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !indirect3v val val val val -> void</span></span>.
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</li><li>(e) <span class="extract"><span class="extract-syntax">primitive !indirect4v val val val val val -> void</span></span>.
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</li><li>(f) <span class="extract"><span class="extract-syntax">primitive !indirect5v val val val val val val -> void</span></span>.
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</li><li>(g) <span class="extract"><span class="extract-syntax">primitive !indirect0 val -> val</span></span>.
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</li><li>(h) <span class="extract"><span class="extract-syntax">primitive !indirect1 val val -> val</span></span>.
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</li><li>(i) <span class="extract"><span class="extract-syntax">primitive !indirect2 val val val -> val</span></span>.
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</li><li>(j) <span class="extract"><span class="extract-syntax">primitive !indirect3 val val val val -> val</span></span>.
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</li><li>(k) <span class="extract"><span class="extract-syntax">primitive !indirect4 val val val val val -> val</span></span>.
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</li><li>(l) <span class="extract"><span class="extract-syntax">primitive !indirect5 val val val val val val -> val</span></span>.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP12" class="paragraph-anchor"></a><b>§12. Control flow. </b>The simplest control statement is an "if". Note that a different primitive
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is used if there is an "else" attached: it would be impossible to use the
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same primitive for both because they couldn't have the same signature.
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</p>
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<p class="commentary"><span class="extract"><span class="extract-syntax">!ifdebug</span></span> is an oddity: it executes the code only if the program is
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being compiled in "debugging mode". (In Inform, that would mean that the
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story file is being made inside the application, or else released in a
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special testing configuration.) While the same effect could be achieved
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using conditional compliation splats, this is much more efficient.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !if val code -> void</span></span>.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !ifelse val code code -> void</span></span>.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !ifdebug code -> void</span></span>.
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</li></ul>
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<p class="commentary">There are then several loops.
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !while val code -> void</span></span>. Similar to <span class="extract"><span class="extract-syntax">while</span></span> in C.
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</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !for val val val code -> void</span></span>. Similar to <span class="extract"><span class="extract-syntax">for</span></span> in C.
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</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !objectloopx ref val code -> void</span></span>. A loop over instances,
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stored in the variable <span class="extract"><span class="extract-syntax">ref</span></span>, of the kind of object <span class="extract"><span class="extract-syntax">val</span></span>.
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</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !objectloop ref val val code -> void</span></span>. A more general form,
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where the secomd <span class="extract"><span class="extract-syntax">val</span></span> is a condition to be evaluated which decides whether
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to execute the code for given <span class="extract"><span class="extract-syntax">ref</span></span> value.
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</li></ul>
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<p class="commentary">A switch statement takes a value, and then executes at most one of an
|
|
arbitrary number of possible code segments. This can't be implemented with
|
|
a single primitive, because its signature would have to be of varying
|
|
lengths with different uses (since some switches have many cases, some few).
|
|
Instead: a <span class="extract"><span class="extract-syntax">switch</span></span> takes a single <span class="extract"><span class="extract-syntax">code</span></span>, but that <span class="extract"><span class="extract-syntax">code</span></span> can in turn
|
|
contain only invocations of <span class="extract"><span class="extract-syntax">!case</span></span>, followed optionally by one of <span class="extract"><span class="extract-syntax">!default</span></span>.
|
|
</p>
|
|
|
|
<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !switch val code -> void</span></span>.
|
|
</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !case val code -> void</span></span>.
|
|
</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !default code -> void</span></span>.
|
|
</li></ul>
|
|
<p class="commentary">This looks a little baroque, but it works in practice:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">inv</span><span class="plain-syntax"> </span><span class="function-syntax">!switch</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> X</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">code</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">inv</span><span class="plain-syntax"> </span><span class="function-syntax">!case</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">code</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">inv</span><span class="plain-syntax"> </span><span class="function-syntax">!print</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_text</span><span class="plain-syntax"> </span><span class="string-syntax">"One!"</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">inv</span><span class="plain-syntax"> </span><span class="function-syntax">!case</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> </span><span class="constant-syntax">2</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">code</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">inv</span><span class="plain-syntax"> </span><span class="function-syntax">!print</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_text</span><span class="plain-syntax"> </span><span class="string-syntax">"Two!"</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">inv</span><span class="plain-syntax"> </span><span class="function-syntax">!default</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">code</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">inv</span><span class="plain-syntax"> </span><span class="function-syntax">!print</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_text</span><span class="plain-syntax"> </span><span class="string-syntax">"Something else!"</span>
|
|
</pre>
|
|
<p class="commentary">As in most C-like languages, there are primitives for:
|
|
</p>
|
|
|
|
<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !break void -> void</span></span>. Exit the innermost switch case or loop.
|
|
</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !continue void -> void</span></span>. Complete the current iteration of
|
|
the innermost loop.
|
|
</li></ul>
|
|
<p class="commentary">Two ways to terminate what's happening:
|
|
</p>
|
|
|
|
<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !return val -> void</span></span>. Finish the current function, giving the
|
|
supplied value as the result if the function is being executed in a value
|
|
context, and throwing it away if not.
|
|
</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !quit void -> void</span></span>. Halt the whole program immediately.
|
|
</li></ul>
|
|
<p class="commentary">And, lastly, the lowest-level way to travel:
|
|
</p>
|
|
|
|
<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !jump lab -> void</span></span>. Jumo to this label in the current function.
|
|
</li></ul>
|
|
<p class="commentary firstcommentary"><a id="SP13" class="paragraph-anchor"></a><b>§13. Interactive fiction-only primitives. </b>The following would make no sense in a general-purpose program. Most mirror
|
|
very low-level I6 features, and Inform uses them mainly when converting
|
|
I6 code into inter: in almost all cases it's better to call routines in the
|
|
template rather than to use these. First, the spatial containment object tree:
|
|
</p>
|
|
|
|
<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !move val val -> void</span></span>. Moves first to second (both are objects).
|
|
</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !in val val -> val</span></span>. Tests if first is in second (both are objects).
|
|
</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !notin val val -> val</span></span>. Negation of same.
|
|
</li></ul>
|
|
<p class="commentary">Object class membership:
|
|
</p>
|
|
|
|
<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !ofclass val val -> val</span></span>. Does the first belong to the enumerated
|
|
subkind whose weak type ID is the second value?
|
|
</li></ul>
|
|
<p class="commentary">Attributes can be handled as follows. The values used to refer to these attributes
|
|
can be inter symbols for their properties, but only if those properties are
|
|
indeed stored as Z-machine or Glulx attributes at run-time.
|
|
</p>
|
|
|
|
<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !give val val -> void</span></span>. Set the second (an attribute) for the first (an object).
|
|
</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !take val val -> void</span></span>. Unset the second (an attribute) for the first (an object).
|
|
</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !has val val -> val</span></span>. Test if the first (an object) has the second (an attibute).
|
|
</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !hasnt val val -> val</span></span>. Negation of same.
|
|
</li></ul>
|
|
<p class="commentary">Direct access to virtual machine object properties:
|
|
</p>
|
|
|
|
<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">primitive !propertyvalue val val -> val</span></span>.
|
|
</li><li>(b) <span class="extract"><span class="extract-syntax">primitive !propertyaddress val val -> val</span></span>.
|
|
</li><li>(c) <span class="extract"><span class="extract-syntax">primitive !propertylength val val -> val</span></span>.
|
|
</li><li>(d) <span class="extract"><span class="extract-syntax">primitive !provides val val -> val</span></span>.
|
|
</li></ul>
|
|
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