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(.module:
[lux (#- case)
[control
["." monad (#+ do)]
["ex" exception (#+ exception:)]]
[data
["." product]
["." error]
["." maybe]
[text
format]
[collection
["." list ("list/" Fold<List> Monoid<List> Functor<List>)]]]
["." macro
["." code]]]
["." // (#+ Pattern Analysis Operation Compiler)
["." scope]
["//." type]
["." structure]
["/." //
["." extension]
[//
["." type
["tc" check]]]]]
[/
["." coverage]])
(exception: #export (cannot-match-type-with-pattern {type Type} {pattern Code})
(ex.report ["Type" (%type type)]
["Pattern" (%code pattern)]))
(exception: #export (sum-type-has-no-case {case Nat} {type Type})
(ex.report ["Case" (%n case)]
["Type" (%type type)]))
(exception: #export (unrecognized-pattern-syntax {pattern Code})
(%code pattern))
(exception: #export (cannot-simplify-type-for-pattern-matching {type Type})
(%type type))
(do-template [<name>]
[(exception: #export (<name> {message Text})
message)]
[cannot-have-empty-branches]
[non-exhaustive-pattern-matching]
)
(def: (re-quantify envs baseT)
(-> (List (List Type)) Type Type)
(.case envs
#.Nil
baseT
(#.Cons head tail)
(re-quantify tail (#.UnivQ head baseT))))
## 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 caseT)
(-> Type (Operation Type))
(loop [envs (: (List (List Type))
(list))
caseT caseT]
(.case caseT
(#.Var id)
(do ///.Monad<Operation>
[?caseT' (//type.with-env
(tc.read id))]
(.case ?caseT'
(#.Some caseT')
(recur envs caseT')
_
(///.throw cannot-simplify-type-for-pattern-matching caseT)))
(#.Named name unnamedT)
(recur envs unnamedT)
(#.UnivQ env unquantifiedT)
(recur (#.Cons env envs) unquantifiedT)
(#.ExQ _)
(do ///.Monad<Operation>
[[ex-id exT] (//type.with-env
tc.existential)]
(recur envs (maybe.assume (type.apply (list exT) caseT))))
(#.Apply inputT funcT)
(.case funcT
(#.Var funcT-id)
(do ///.Monad<Operation>
[funcT' (//type.with-env
(do tc.Monad<Check>
[?funct' (tc.read funcT-id)]
(.case ?funct'
(#.Some funct')
(wrap funct')
_
(tc.throw cannot-simplify-type-for-pattern-matching caseT))))]
(recur envs (#.Apply inputT funcT')))
_
(.case (type.apply (list inputT) funcT)
(#.Some outputT)
(recur envs outputT)
#.None
(///.throw cannot-simplify-type-for-pattern-matching caseT)))
(#.Product _)
(|> caseT
type.flatten-tuple
(list/map (re-quantify envs))
type.tuple
(:: ///.Monad<Operation> wrap))
_
(:: ///.Monad<Operation> wrap (re-quantify envs caseT)))))
(def: (analyse-primitive type inputT cursor output next)
(All [a] (-> Type Type Cursor Pattern (Operation a) (Operation [Pattern a])))
(//.with-cursor cursor
(do ///.Monad<Operation>
[_ (//type.with-env
(tc.check inputT type))
outputA next]
(wrap [output outputA]))))
## 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 (Operation a) (Operation [Pattern a])))
(.case pattern
[cursor (#.Symbol ["" name])]
(//.with-cursor cursor
(do ///.Monad<Operation>
[outputA (scope.with-local [name inputT]
next)
idx scope.next-local]
(wrap [(#//.Bind idx) outputA])))
(^template [<type> <input> <output>]
[cursor <input>]
(analyse-primitive <type> inputT cursor (#//.Simple <output>) next))
([Bit (#.Bit pattern-value) (#//.Bit pattern-value)]
[Nat (#.Nat pattern-value) (#//.Nat pattern-value)]
[Int (#.Int pattern-value) (#//.Int pattern-value)]
[Rev (#.Rev pattern-value) (#//.Rev pattern-value)]
[Frac (#.Frac pattern-value) (#//.Frac pattern-value)]
[Text (#.Text pattern-value) (#//.Text pattern-value)]
[Any (#.Tuple #.Nil) #//.Unit])
(^ [cursor (#.Tuple (list singleton))])
(analyse-pattern #.None inputT singleton next)
[cursor (#.Tuple sub-patterns)]
(//.with-cursor cursor
(do ///.Monad<Operation>
[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 (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 (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] (Operation [(List Pattern) a])
(Operation [(List Pattern) a])))
(function (_ [memberT memberC] then)
(do @
[[memberP [memberP+ thenA]] ((:coerce (All [a] (-> (Maybe Nat) Type Code (Operation a) (Operation [Pattern a])))
analyse-pattern)
#.None memberT memberC then)]
(wrap [(list& memberP memberP+) thenA]))))
(do @
[nextA next]
(wrap [(list) nextA]))
(list.reverse matches))]
(wrap [(//.product-pattern memberP+)
thenA])))
_
(///.throw cannot-match-type-with-pattern [inputT pattern])
)))
[cursor (#.Record record)]
(do ///.Monad<Operation>
[record (structure.normalize record)
[members recordT] (structure.order record)
_ (//type.with-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<Operation>
[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))
(do ///.Monad<Operation>
[[testP nextA] (if (and (n/> num-cases size-sum)
(n/= (dec num-cases) idx))
(analyse-pattern #.None
(type.variant (list.drop (dec num-cases) flat-sum))
(` [(~+ values)])
next)
(analyse-pattern #.None case-type (` [(~+ values)]) next))]
(wrap [(//.sum-pattern num-cases idx testP)
nextA]))
_
(///.throw sum-type-has-no-case [idx inputT])))
_
(///.throw cannot-match-type-with-pattern [inputT pattern]))))
(^ [cursor (#.Form (list& [_ (#.Tag tag)] values))])
(//.with-cursor cursor
(do ///.Monad<Operation>
[tag (extension.lift (macro.normalize tag))
[idx group variantT] (extension.lift (macro.resolve-tag tag))
_ (//type.with-env
(tc.check inputT variantT))]
(analyse-pattern (#.Some (list.size group)) inputT (` ((~ (code.nat idx)) (~+ values))) next)))
_
(///.throw unrecognized-pattern-syntax pattern)
))
(def: #export (case analyse inputC branches)
(-> Compiler Code (List [Code Code]) (Operation Analysis))
(.case branches
#.Nil
(///.throw cannot-have-empty-branches "")
(#.Cons [patternH bodyH] branchesT)
(do ///.Monad<Operation>
[[inputT inputA] (//type.with-inference
(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 coverage.determine)
outputTC (monad.map @ (|>> product.left coverage.determine) outputT)
_ (.case (monad.fold error.Monad<Error> coverage.merge outputHC outputTC)
(#error.Success coverage)
(///.assert non-exhaustive-pattern-matching ""
(coverage.exhaustive? coverage))
(#error.Error error)
(///.fail error))]
(wrap (#//.Case inputA [outputH outputT])))))
|