allow implicit parameter bindings in patterns

It could work like such:

main = do
    ?conts <- getContents
    fun

fun :: (?conts :: String) -> IO ()
fun = ...

becoming something like

main = do
    conts <- getContents
    let ?conts = conts
    fun

Of course there are still questions regarding interactions with pattern guards and view patterns (whether those variables should be in scope for other guards, or for view patterns that follow).

This interaction with view patterns (and pattern guards), should likely elicit a warning:

   let ?x = 1 in
   let f ?x ((?x +) -> y) = y in
   f 0 0

As it might be expected that this expression should be 1, while I think it should evaluate to 0.

This probably would lead to more syntax stealing, but it seems unlikely that there would be code that enables -XImplicitParams that does stuff like:

x ?y = ...

Expecting to define the function `?', rather than binding the implicit parameter ?y.

Trac metadata

Trac field	Value
Version	6.12.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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