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130 lines
3.5 KiB
HTML
130 lines
3.5 KiB
HTML
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<html>
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<head>
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<title>
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Promise Ex Declarations
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</title>
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</head>
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<body
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bgcolor="#ffffff"
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text="#000000"
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>
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<hr>
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<!-------------------------->
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<h1> Promise Ex Declarations</h1>
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This document is a description of promise ex declarations,
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which are currently unfinished and as such are undocumented
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in the reference manual.
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<p>
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<hr>
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<!-------------------------->
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<h2> Syntax </h2>
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There are currently three promise ex declarations: promise_exclusive,
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promise_exhaustive, and promise_exclusive_exhaustive. They are used to
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denote determinism properties of a disjunction, and denote either exclusivity
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exhaustiveness or both. The examples of each, given below, also show
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the different ways that existential quantification can be handled.
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<ul>
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<li> Mutual exclusivity:
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<pre>
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:- all [X, Y] promise_exclusive
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some [Z] (
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p(X, Y, Z)
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;
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q(X, Y, Z)
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).
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</pre>
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<li> Exhaustiveness:
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<pre>
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:- all [X] promise_exhaustive
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(
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p(X, _)
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;
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q(X, _)
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).
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</pre>
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<li> Both together:
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<pre>
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:- all [X] promise_exclusive_exhaustive
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some [Y] (
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p(X, Y)
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;
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q(X, Y, Z)
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).
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</pre>
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</ul>
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All three declarations are restricted in the following ways:
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<ol>
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<li> Any variable that occurs in more than one disjunct must be
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explicitly quantified.
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<li> Any variable occuring in only one disjunct is existentially quantified.
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This is similarly applicable when an underscore is used in place of a
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variable.
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</ol>
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<p>
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<hr>
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<!-------------------------->
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<h2> Development </h2>
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This tracks the use of promise ex declarations through the compiler, and
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may be useful as a quick summary of the current state of development. Items
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marked with an asterisk (*) are not yet implemented. Places where data
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structures etc. have been defined are in italics.
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<ol>
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<li> the declarations enter the parse tree
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<ul>
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<li> <i>the operators are defined</i> (library/ops.m)
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<li> <i>the structure for promise ex declarations in the parse tree
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is defined</i> (prog_data.m)
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<li> they are parsed and entered into the parse tree (prog_io.m)
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</ul>
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<li> they may be pretty printed (mercury_to_mercury.m, prog_out.m).
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<li> they are error checked, and entered in to the HLDS as
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dummy predicates
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<ul>
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<li> error checking (make_hlds.m)
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<li> entering of declarations into the HLDS as dummy predicates
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(make_hlds.m)
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</ul>
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<li> go through typechecking as predicates; after typechecking they
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are removed from processing as predicates and entered into the
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appropriate table in the HLDS
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<ul>
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<li> post typechecking processing initiated for promise ex
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declarations (purity.m)
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<li> promise_exlusive and promise_exhaustive declarations are
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indexed by the predicate calls made in them in the exclusive
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table (post_typecheck.m)
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<li> <i>definition of exclusive table as part of HLDS, and
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operations on the table </i>
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(hlds_module.m)
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<li> (*) where a promise_exhaustive declaration is paired with a
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promise_exclusive declaration, they are merged into a
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promise_exclusive_exhaustive declaration; otherwise the
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promise_exhaustive declartion is entered in the exhaustive
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table of the HLDS (post_typecheck.m)
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<li> (*) <i>definition of exhaustive table as part of HLDS, and
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operations on the table </i>
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(hlds_module.m)
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</ul>
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<li> (*) exclusivity information is used during switch detection, and
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where it leads to a full switch being made, applicable exhaustiveness
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information is also used (switch_detection.m)
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<li> (*) exhaustiveness information is used during determinism analysis
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(det_analysis.m) or as an add-on to switch detection
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(switch_detection.m)
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</ol>
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</body>
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</html>
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