Tomasz Zielonka wrote:
On Tue, Nov 08, 2005 at 02:43:47PM +0000, Malcolm Wallace wrote:
Of course, there is the old stand-by C pre-processor trick:
#define superError(s) error (s++"\nin file "++__FILE__ \
++" at line "++__LINE__)
There is a nice trick I saw in darcs' code to make this even more
Haskellish:
#define superError (\s -> error (s++"\nin file "++ __FILE__ \
++" at line "++ show (__LINE__ :: Int)))
so you can simply write:
superError "message"
Don't you also need to define "head" as a CPP macro (otherwise you'll
just get the location of "head",
and I'm sure you know where to find that already)?
#define head (\xs -> case xs of { (x:_) -> x ; _ -> superError "head:
empty list"})
Unfortunately, I don't think CPP will play nicely with operators like ! :-(
There really should be a better way to do this, "head: empty list",
"read: no parse" etc is high on my list of Haskell annoyances.
-k
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