#1171: GHC doesn't respect the imprecise exceptions semantics
----------------------+-----------------------------------------------------
Reporter: neil | Owner:
Type: bug | Status: reopened
Priority: low | Milestone: _|_
Component: Compiler | Version: 6.6
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: cg059 | Architecture: Multiple
Os: Multiple |
----------------------+-----------------------------------------------------
Comment (by Isaac Dupree):
Stefan O'Rear happened to write in haskell-cafe a performance reason for
allowing non-termination to throw any exception:
"When you see an expression of the form:
f a
you generally want to evaluate a before applying; but if a is _|_, this
will only give the correct result if f a = _|_. Merely 'guaranteed to
evaluate' misses out on some common cases, for instance ifac:
{{{
ifac 0 a = a
ifac n a = ifac (n - 1) (a * n)
}}}
ifac is guaranteed to either evaluate a, or go into an infinite loop -
so it can be found strict, and unboxed. Whereas 'ifac -1 (error "moo")'
is an infinite loop, so using a definition based on evaluation misses
this case."
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1171#comment:13>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
