Specialise broken for implicit parameters

[pcapriotti]

The tcrun019 test case is failing with optimization on. Here is an even simpler test case:

{-# LANGUAGE ImplicitParams, RankNTypes #-}

module Main where

f :: (?x :: Int) => ((?x :: Int) => Int) -> Bool -> Int
f g False = g
f g True = let ?x = ?x + 1
           in f g False

h :: (?x :: Int) => Int
h = ?x

main :: IO ()
main = print (let ?x = 0 in f h True)

What happens is that f gets incorrectly specialized, and, as a result, the recursive call to f uses the old binding for the implicit parameter.

I think the problem was introduced with the refactoring in 5a8ac0f823c151c062a3f1903574030423bb255c, which broke the test for implicit parameter constraints in Specialise.lhs.

The attached patch seems to fix it.

[simonpj@…]

commit 2f08f709cfdace23a4e32d80a57af349f7cc785a

Author: Simon Peyton Jones <simonpj@microsoft.com>
Date:   Thu Aug 23 16:35:55 2012 +0100

    Don't specialise on implicit-parameter arguments in Specalise
    
    This is a fix for Trac #7101

 compiler/specialise/Specialise.lhs |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

[simonpj]

Good catch Paolo!

[pcapriotti]

Merged as 20b25bc688b7a6257cb466d9c70c214dafa369c6.