unreachable GADT pattern clauses show up as warnings with -Wall
In the following code, there is a line commented out. With it commented out, I get the following warning:
patternbug.hs:10:0:
Warning: Pattern match(es) are non-exhaustive
In the definition of `interpret': Patterns not matched: EVar
With it uncommented, I get the following compiler error:
patternbug.hs:11:10:
Inaccessible case alternative: Can't match types `()' and `(a, vs)'
In the pattern: EVar
In the definition of `interpret':
interpret EVar = error "unreachable"
The exhaustive pattern-matching algorithm should ignore unreachable cases in its analysis.
{-# OPTIONS_GHC -Wall #-}
{-# LANGUAGE GADTs #-}
module PatternBug where
data Expr a vs where
EPrim :: String -> a -> Expr a vs
EVar :: Expr a (a,vs)
interpret :: Expr a () -> a
interpret (EPrim _ a) = a
-- interpret EVar = error "unreachable"
Trac metadata
Trac field | Value |
---|---|
Version | 6.8.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | ryani.spam@gmail.com |
Operating system | Unknown |
Architecture | Unknown |