An overview of the assertions module's role and abilities.
§1. Prerequisites. The assertions module is a part of the Inform compiler toolset. It is presented as a literate program or "web". Before diving in:
- (a) It helps to have some experience of reading webs: see inweb for more.
- (b) The module is written in C, in fact ANSI C99, but this is disguised by the fact that it uses some extension syntaxes provided by the inweb literate programming tool, making it a dialect of C called InC. See inweb for full details, but essentially: it's C without predeclarations or header files, and where functions have names like Tags::add_by_name rather than just add_by_name.
- (c) This module uses other modules drawn from the compiler, and also uses a module of utility functions called foundation. For more, see A Brief Guide to Foundation (in foundation).
§2. Assertions. Top-level declarations are dealt with thus:
- ● The tree is subdivided into //runtime: Compilation Units//. The project's own source text is one unit, as is each extension used.
- ● A minimal set of kinds, such as "number", verbs, such as "to mean", relations, such as "meaning", and so on, is created. See in particular Booting Verbs (in assertions).
- ● Three passes are made through the "major nodes" of the parse tree, meaning,
assertion sentences and top-level declarations of structures such as tables,
equations and rules. See Passes through Major Nodes.
- (0) During the "pre-pass" names of tables and other top-level structures are recorded, and sentences are classified by Classifying::sentence. This is done by asking the linguistics module to diagram them and determine whether the meaning is "regular" — a typical sentence asserting some relationship, such as "the ball is on the table" — or "special" — a sentence with some other purpose, such as "Test ... with ...", often but not always written in the imperative.
- (1) During "pass 1", noun phrases in these assertion sentences are understood, which may involve creating new instances or other values. For example, the sentence "The fedora hat is on the can of Ubuntu cola" may cause new instances "fedora hat" and "can of Ubuntu cola" to be created. This process is called "refinement": see Refine Parse Tree, which calls The Creator to bring things into being.1 The function Assertions::make_coupling is then called to draw out information from this pairing of values.
- (2) During "pass 2", Assertions::make_coupling is again called, and this time is able to draw out relationships between values: for example, that the hat is indeed spatially on top of the can.
Classification: SENTENCE_NT'jane is a woman' VERB_NT'is' {verb 'be' 3p s act IS_TENSE +ve} UNPARSED_NOUN_NT'jane' UNPARSED_NOUN_NT'woman' {indefinite 'a' n/m/f nom/acc s} Refined: CREATED_NT'jane' COMMON_NOUN_NT'woman' {indefinite 'a' n/m/f nom/acc s} {creation: << woman(x) >>} {eval: TEST_VALUE_NT} After creation: SENTENCE_NT'jane is a woman' VERB_NT'is' {verb 'be' 3p s act IS_TENSE +ve} PROPER_NOUN_NT'jane' {eval: CONSTANT_NT'jane' {kind: object} {instance: 'jane'}} {created here} COMMON_NOUN_NT'woman' {indefinite 'a' n/m/f nom/acc s} {creation: << woman(x) >>} {eval: TEST_VALUE_NT}