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Improve message for errors when unifying rigid type variables

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Evan Czaplicki 2013-12-12 17:11:49 -08:00
parent 91007fc4f9
commit 6ff938c7cf
1 changed files with 9 additions and 3 deletions
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12
compiler/Type/Unify.hs
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@ -111,9 +111,15 @@ actuallyUnify span variable1 variable2 = do
_ -> comparableError Nothing
rigidError variable = TS.addError span (Just hint) variable1 variable2
where hint = "There is a problem with the '" ++
render (pretty Never variable) ++
"' in the type signature. It currently is not possible to unify type variables that appear in top-level declarations and again in subexpressions"
where
var = "'" ++ render (pretty Never variable) ++ "'"
hint = concat
[ "This probably relates to a type annotation. A type "
, "annotation may say ", var, " but should be a more "
, "specific type. Also, type variables are not "
, "shared between type annotations, so ", var, " in one "
, "is not the same as " ++ var ++ " in another. "
, "Something like that happened" ]
superUnify =
case (flex desc1, flex desc2, name desc1, name desc2) of