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implementation module Snug.Compile.Typing
import Data.Error
import Snug.Syntax
instance type Expression
where
type locals e = case e of
BasicValue bv ->
type locals bv
Symbol sym -> // TODO
Constructor cons ->
lookupConstructorM ns cons >>= \(ConstructorDef _ args ret) ->
foldr TyFun ret args
Case _ alts ->
checkSameTypes "case alternatives" [type locals e \\ CaseAlternative _ e <- alts]
ExpApp e1 e2 ->
type locals e1 >>= \t1 -> case t1 of
TyFun t1arg t1ret ->
type locals e2 >>= \t2 ->
unify t1arg t2 ->
resolve t1ret
TyVar _ ->
freshTyVar >>= \t1arg ->
freshTyVar >>= \t1ret ->
unify t1arg t2 ->
resolve t1ret
_ ->
fail "ExpApp: first argument cannot be unified with a function type"
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