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(;module:
lux
(lux (control [monad #+ do]
["ex" exception #+ exception:]
eq)
(data [bool]
[number]
[product]
["e" error]
[maybe]
[text]
text/format
(coll [list "list/" Fold<List> Monoid<List> Functor<List>]))
[meta]
(meta [code]
[type]
(type ["tc" check])))
(luxc ["&" base]
(lang ["la" analysis]
(analysis [";A" common]
[";A" structure]
(case [";A" coverage])))
["&;" scope]))
(exception: #export Cannot-Match-Type-With-Pattern)
(exception: #export Sum-Type-Has-No-Case)
(exception: #export Unrecognized-Pattern-Syntax)
(exception: #export Cannot-Simplify-Type-For-Pattern-Matching)
(def: (pattern-error type pattern)
(-> Type Code Text)
(Cannot-Match-Type-With-Pattern
(format " Type: " (%type type) "\n"
"Pattern: " (%code pattern))))
## Type-checking on the input value is done during the analysis of a
## "case" expression, to ensure that the patterns being used make
## sense for the type of the input value.
## Sometimes, that input value is complex, by depending on
## type-variables or quantifications.
## This function makes it easier for "case" analysis to properly
## type-check the input with respect to the patterns.
(def: (simplify-case-type type)
(-> Type (Meta Type))
(case type
(#;Var id)
(do meta;Monad<Meta>
[? (&;with-type-env
(tc;bound? id))]
(if ?
(do @
[type' (&;with-type-env
(tc;read id))]
(simplify-case-type type'))
(&;throw Cannot-Simplify-Type-For-Pattern-Matching (%type type))))
(#;Named name unnamedT)
(simplify-case-type unnamedT)
(^or (#;UnivQ _) (#;ExQ _))
(do meta;Monad<Meta>
[[ex-id exT] (&;with-type-env
tc;existential)]
(simplify-case-type (maybe;assume (type;apply (list exT) type))))
(#;Apply inputT funcT)
(case (type;apply (list inputT) funcT)
(#;Some outputT)
(:: meta;Monad<Meta> wrap outputT)
#;None
(&;fail (format "Cannot apply type " (%type funcT) " to type " (%type inputT))))
_
(:: meta;Monad<Meta> wrap type)))
## This function handles several concerns at once, but it must be that
## way because those concerns are interleaved when doing
## pattern-matching and they cannot be separated.
## The pattern is analysed in order to get a general feel for what is
## expected of the input value. This, in turn, informs the
## type-checking of the input.
## A kind of "continuation" value is passed around which signifies
## what needs to be done _after_ analysing a pattern.
## In general, this is done to analyse the "body" expression
## associated to a particular pattern _in the context of_ said
## pattern.
## The reason why *context* is important is because patterns may bind
## values to local variables, which may in turn be referenced in the
## body expressions.
## That is why the body must be analysed in the context of the
## pattern, and not separately.
(def: (analyse-pattern num-tags inputT pattern next)
(All [a] (-> (Maybe Nat) Type Code (Meta a) (Meta [la;Pattern a])))
(case pattern
[cursor (#;Symbol ["" name])]
(&;with-cursor cursor
(do meta;Monad<Meta>
[outputA (&scope;with-local [name inputT]
next)
idx &scope;next-local]
(wrap [(` ("lux case bind" (~ (code;nat idx)))) outputA])))
[cursor (#;Symbol ident)]
(&;with-cursor cursor
(&;fail (format "Symbols must be unqualified inside patterns: " (%ident ident))))
(^template [<type> <code-tag>]
[cursor (<code-tag> test)]
(&;with-cursor cursor
(do meta;Monad<Meta>
[_ (&;with-type-env
(tc;check inputT <type>))
outputA next]
(wrap [pattern outputA]))))
([Bool #;Bool]
[Nat #;Nat]
[Int #;Int]
[Deg #;Deg]
[Frac #;Frac]
[Text #;Text])
(^ [cursor (#;Tuple (list))])
(&;with-cursor cursor
(do meta;Monad<Meta>
[_ (&;with-type-env
(tc;check inputT Unit))
outputA next]
(wrap [(` ("lux case tuple" [])) outputA])))
(^ [cursor (#;Tuple (list singleton))])
(analyse-pattern #;None inputT singleton next)
[cursor (#;Tuple sub-patterns)]
(&;with-cursor cursor
(do meta;Monad<Meta>
[inputT' (simplify-case-type inputT)]
(case inputT'
(#;Product _)
(let [sub-types (type;flatten-tuple inputT')
num-sub-types (maybe;default (list;size sub-types)
num-tags)
num-sub-patterns (list;size sub-patterns)
matches (cond (n.< num-sub-types num-sub-patterns)
(let [[prefix suffix] (list;split (n.dec num-sub-patterns) sub-types)]
(list;zip2 (list/compose prefix (list (type;tuple suffix))) sub-patterns))
(n.> num-sub-types num-sub-patterns)
(let [[prefix suffix] (list;split (n.dec num-sub-types) sub-patterns)]
(list;zip2 sub-types (list/compose prefix (list (code;tuple suffix)))))
## (n.= num-sub-types num-sub-patterns)
(list;zip2 sub-types sub-patterns)
)]
(do @
[[memberP+ thenA] (list/fold (: (All [a]
(-> [Type Code] (Meta [(List la;Pattern) a])
(Meta [(List la;Pattern) a])))
(function [[memberT memberC] then]
(do @
[[memberP [memberP+ thenA]] ((:! (All [a] (-> (Maybe Nat) Type Code (Meta a) (Meta [la;Pattern a])))
analyse-pattern)
#;None memberT memberC then)]
(wrap [(list& memberP memberP+) thenA]))))
(do @
[nextA next]
(wrap [(list) nextA]))
(list;reverse matches))]
(wrap [(` ("lux case tuple" [(~@ memberP+)]))
thenA])))
_
(&;fail (pattern-error inputT pattern))
)))
[cursor (#;Record record)]
(do meta;Monad<Meta>
[record (structureA;normalize record)
[members recordT] (structureA;order record)
_ (&;with-type-env
(tc;check inputT recordT))]
(analyse-pattern (#;Some (list;size members)) inputT [cursor (#;Tuple members)] next))
[cursor (#;Tag tag)]
(&;with-cursor cursor
(analyse-pattern #;None inputT (` ((~ pattern))) next))
(^ [cursor (#;Form (list& [_ (#;Nat idx)] values))])
(&;with-cursor cursor
(do meta;Monad<Meta>
[inputT' (simplify-case-type inputT)]
(case inputT'
(#;Sum _)
(let [flat-sum (type;flatten-variant inputT')
size-sum (list;size flat-sum)
num-cases (maybe;default size-sum num-tags)]
(case (list;nth idx flat-sum)
(^multi (#;Some case-type)
(n.< num-cases idx))
(if (and (n.> num-cases size-sum)
(n.= (n.dec num-cases) idx))
(do meta;Monad<Meta>
[[testP nextA] (analyse-pattern #;None
(type;variant (list;drop (n.dec num-cases) flat-sum))
(` [(~@ values)])
next)]
(wrap [(` ("lux case variant" (~ (code;nat idx)) (~ (code;nat num-cases)) (~ testP)))
nextA]))
(do meta;Monad<Meta>
[[testP nextA] (analyse-pattern #;None case-type (` [(~@ values)]) next)]
(wrap [(` ("lux case variant" (~ (code;nat idx)) (~ (code;nat num-cases)) (~ testP)))
nextA])))
_
(&;throw Sum-Type-Has-No-Case
(format "Case: " (%n idx) "\n"
"Type: " (%type inputT)))))
_
(&;fail (pattern-error inputT pattern)))))
(^ [cursor (#;Form (list& [_ (#;Tag tag)] values))])
(&;with-cursor cursor
(do meta;Monad<Meta>
[tag (meta;normalize tag)
[idx group variantT] (meta;resolve-tag tag)
_ (&;with-type-env
(tc;check inputT variantT))]
(analyse-pattern (#;Some (list;size group)) inputT (` ((~ (code;nat idx)) (~@ values))) next)))
_
(&;throw Unrecognized-Pattern-Syntax (%code pattern))
))
(def: #export (analyse-case analyse inputC branches)
(-> &;Analyser Code (List [Code Code]) (Meta la;Analysis))
(case branches
#;Nil
(&;fail "Cannot have empty branches in pattern-matching expression.")
(#;Cons [patternH bodyH] branchesT)
(do meta;Monad<Meta>
[[inputT inputA] (commonA;with-unknown-type
(analyse inputC))
outputH (analyse-pattern #;None inputT patternH (analyse bodyH))
outputT (monad;map @
(function [[patternT bodyT]]
(analyse-pattern #;None inputT patternT (analyse bodyT)))
branchesT)
outputHC (|> outputH product;left coverageA;determine)
outputTC (monad;map @ (|>. product;left coverageA;determine) outputT)
_ (case (monad;fold e;Monad<Error> coverageA;merge outputHC outputTC)
(#e;Success coverage)
(if (coverageA;exhaustive? coverage)
(wrap [])
(&;fail "Pattern-matching is not exhaustive."))
(#e;Error error)
(&;fail error))]
(wrap (` ("lux case" (~ inputA) (~ (code;record (list& outputH outputT)))))))))
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