Bang pattern doesn't work on a newtype constructor
According to the documentation, f0
and f1
in the following program should have the identical semantics:
{-# LANGUAGE BangPatterns #-}
module Main where
newtype N = N Int
f0 :: N -> Int
f0 n = case n of
!(N _) -> 0
_ -> 1
f1 :: N -> Int
f1 n = n `seq` case n of
N _ -> 0
_ -> 1
main = do
print $ f0 undefined
print $ f1 undefined
However, ghc only compiles f1
into a strict function:
% ./bang-newtype
0
bang-newtype: Prelude.undefined
Trac metadata
Trac field | Value |
---|---|
Version | 7.8.3 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |