-XBlockArguments: Avoid Lambda incorrect

[MangoIV]

• avoid lambda with BlockArguments doesn't insert parens resulting in an error when applying the hint
• if BlockArguments are on, it should be checkd if the lambda is in parens and if that's not the case, automatically surround the eta reduced expressions with parens.

[zliu41]

Some examples would be helpful!

[MangoIV]

Before applying the hint:

{-# LANGUAGE BlockArguments #-}
module BlockArgumentsHlint where

g :: Int -> a -> Bool
g _ _ = True

r :: (Int -> Bool) -> (Int -> Bool)
r = id

f :: Int -> Bool
f = r \x -> g 3 x

after applying the hint:

{-# LANGUAGE BlockArguments #-}
module BlockArgumentsHlint where

g :: Int -> a -> Bool
g _ _ = True

r :: (Int -> Bool) -> (Int -> Bool)
r = id

f :: Int -> Bool
f = r g 3

[MangoIV]

now r takes two arguments when it should actually take only one, what it should do is insert parenthesis around g 3

[MangoIV]

so the correct refactoring would be

{-# LANGUAGE BlockArguments #-}
module BlockArgumentsHlint where

g :: Int -> a -> Bool
g _ _ = True

r :: (Int -> Bool) -> (Int -> Bool)
r = id

f :: Int -> Bool
f = r (g 3)

[zliu41]

Thanks! This seems more involved than a good first issue, and may or may not have to do with apply-refact. Will have a closer look later.

[andreasabel]

Here is an instance I encountered while working in vscode with the hls:

localScope x v = local \ env -> Map.insert x v env

The hint is

Avoid lambda
Found:
\ env -> Map.insert x v env
Why not:
Map.insert x v

If I apply this hint, I am getting the incorrect

localScope x v = local Map.insert x v

A $ is needed after local or (less preferable) parentheses.

[zliu41]

Fix: #1634

[MangoIV]

Thank you for fixing this! ❤️

[zliu41]

@MangoIV Thanks for the bug report. Sorry for the delay, it totally slipped my mind.