Ambiguous infix expression

[YurasShumovich]

Updating from HSE-1.3.4 to HSE-1.8.2 I found that the next module can't be parsed with new version:

module Main
where

import Control.Arrow

doSth = (+ 1) . head &&& tail

The old version parses the code successfully.

ghc-6.10.4 on Mac OS X 10.5.8

[nibro]

The reason for the perceived regression is that 1.3.4 didn't handle fixities properly, while 1.8.2 does. By default, HSE is aware of only the fixities defined in the Prelude, where . is infixr 9. Any unrecognized operators are defaulted to infixl 9, which makes the example expression ambiguous.

The fix is to either not care about fixities at all (parseFileWithMode (defaultParseMode { fixities = [] } ), which gives back the old behavior and treats both . and &&& as infixl 9. Or (more correct) to make HSE aware of all base fixities (parseFileWithMode (defaultParseMode { fixities = baseFixities } ), so that &&& is correctly treated a infixr 3.