Make HsIf more polymorphic with RebindableSyntax
Currently, ifThenElse is typed this way:
ifThenElse :: pred_ty -> b_ty -> b_ty -> res_ty
I propose to change this to:
ifThenElse :: pred_ty -> b1_ty -> b2_ty -> res_ty
to support expressions like this:
ifThenElse :: Maybe a -> (a -> b) -> b -> b
ifThenElse (Just a) f _ = f a
ifThenElse Nothing _ e = e
example :: String
example = if Just 2
then \v -> show v
else "No value"
The fix is very simple and just one more line to add to the typechecker. Patch is attached.
Trac metadata
Trac field | Value |
---|---|
Version | 7.0.1 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |