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(;module:
lux
(lux (control [monad #+ do]
eq)
(data [bool "B/" Eq<Bool>]
[number]
[text]
text/format
[product]
["R" result "R/" Monad<Result>]
(coll [list "L/" Fold<List> Monoid<List> Monad<List>]
["D" dict]))
[macro #+ Monad<Lux>]
(macro [code])
[type]
(type ["TC" check]))
(../.. ["&" base]
(lang ["la" analysis])
["&;" env])
(.. ["&;" common]
["&;" structure])
(. ["&&;" coverage]))
(def: (pattern-error type pattern)
(-> Type Code Text)
(format "Cannot match this type: " (%type type) "\n"
" With this 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 (Lux Type))
(case type
(#;Var id)
(do Monad<Lux>
[? (&;within-type-env
(TC;bound? id))]
(if ?
(do @
[type' (&;within-type-env
(TC;read-var id))]
(simplify-case-type type'))
(&;fail (format "Cannot simplify type for pattern-matching: " (%type type)))))
(#;Named name unnamedT)
(simplify-case-type unnamedT)
(^or (#;UnivQ _) (#;ExQ _))
(do Monad<Lux>
[[ex-id exT] (&;within-type-env
TC;existential)]
(simplify-case-type (assume (type;apply (list exT) type))))
_
(:: Monad<Lux> 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 (Lux a) (Lux [la;Pattern a])))
(case pattern
[cursor (#;Symbol ["" name])]
(&;with-cursor cursor
(do Monad<Lux>
[outputA (&env;with-local [name inputT]
next)
idx &env;next-local]
(wrap [(#la;BindP idx) outputA])))
[cursor (#;Symbol ident)]
(&;with-cursor cursor
(&;fail (format "Symbols must be unqualified inside patterns: " (%ident ident))))
(^template [<type> <code-tag> <pattern-tag>]
[cursor (<code-tag> test)]
(&;with-cursor cursor
(do Monad<Lux>
[_ (&;within-type-env
(TC;check inputT <type>))
outputA next]
(wrap [(<pattern-tag> test) outputA]))))
([Bool #;Bool #la;BoolP]
[Nat #;Nat #la;NatP]
[Int #;Int #la;IntP]
[Deg #;Deg #la;DegP]
[Frac #;Frac #la;FracP]
[Text #;Text #la;TextP])
(^ [cursor (#;Tuple (list))])
(&;with-cursor cursor
(do Monad<Lux>
[_ (&;within-type-env
(TC;check inputT Unit))
outputA next]
(wrap [(#la;TupleP (list)) outputA])))
(^ [cursor (#;Tuple (list singleton))])
(analyse-pattern #;None inputT singleton next)
[cursor (#;Tuple sub-patterns)]
(&;with-cursor cursor
(do Monad<Lux>
[inputT' (simplify-case-type inputT)]
(case inputT'
(#;Product _)
(let [sub-types (type;flatten-tuple inputT)
num-sub-types (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 (L/append 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 (L/append prefix (list (code;tuple suffix)))))
## (n.= num-sub-types num-sub-patterns)
(list;zip2 sub-types sub-patterns)
)]
(do @
[[memberP+ thenA] (L/fold (: (All [a]
(-> [Type Code] (Lux [(List la;Pattern) a])
(Lux [(List la;Pattern) a])))
(function [[memberT memberC] then]
(do @
[[memberP [memberP+ thenA]] ((:! (All [a] (-> (Maybe Nat) Type Code (Lux a) (Lux [la;Pattern a])))
analyse-pattern)
#;None memberT memberC then)]
(wrap [(list& memberP memberP+) thenA]))))
(do @
[nextA next]
(wrap [(list) nextA]))
matches)]
(wrap [(#la;TupleP memberP+) thenA])))
_
(&;fail (pattern-error inputT pattern))
)))
[cursor (#;Record record)]
(do Monad<Lux>
[record (&structure;normalize record)
[members recordT] (&structure;order record)
_ (&;within-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 Monad<Lux>
[inputT' (simplify-case-type inputT)]
(case inputT'
(#;Sum _)
(let [flat-sum (type;flatten-variant inputT)
size-sum (list;size flat-sum)
num-cases (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 Monad<Lux>
[[testP nextA] (analyse-pattern #;None
(type;variant (list;drop (n.dec num-cases) flat-sum))
(` [(~@ values)])
next)]
(wrap [(#la;VariantP idx num-cases testP)
nextA]))
(do Monad<Lux>
[[testP nextA] (analyse-pattern #;None case-type (` [(~@ values)]) next)]
(wrap [(#la;VariantP idx num-cases testP)
nextA])))
_
(&;fail (format "Cannot match index " (%n idx) " against type: " (%type inputT)))))
_
(&;fail (pattern-error inputT pattern)))))
(^ [cursor (#;Form (list& [_ (#;Tag tag)] values))])
(&;with-cursor cursor
(do Monad<Lux>
[tag (macro;normalize tag)
[idx group variantT] (macro;resolve-tag tag)
_ (&;within-type-env
(TC;check inputT variantT))]
(analyse-pattern (#;Some (list;size group)) inputT (` ((~ (code;nat idx)) (~@ values))) next)))
_
(&;fail (format "Unrecognized pattern syntax: " (%code pattern)))
))
(def: #export (analyse-case analyse input branches)
(-> &;Analyser Code (List [Code Code]) (Lux la;Analysis))
(case branches
#;Nil
(&;fail "Cannot have empty branches in pattern-matching expression.")
(#;Cons [patternH bodyH] branchesT)
(do Monad<Lux>
[[inputT inputA] (&common;with-unknown-type
(analyse input))
outputH (analyse-pattern #;None inputT patternH (analyse bodyH))
outputT (monad;map @
(function [[patternT bodyT]]
(analyse-pattern #;None inputT patternT (analyse bodyT)))
branchesT)
_ (case (monad;fold R;Monad<Result>
&&coverage;merge
(|> outputH product;left &&coverage;determine)
(L/map (|>. product;left &&coverage;determine) outputT))
(#R;Success coverage)
(if (&&coverage;total? coverage)
(wrap [])
(&;fail "Pattern-matching is not total."))
(#R;Error error)
(&;fail error))]
(wrap (#la;Case inputA (#;Cons outputH outputT))))))
|
