28 Apr
2008
28 Apr
'08
9:02 p.m.
Hi
The first case makes sense, and is just a RULE. Though it seems GHC already does this?
g = head ""
goes to:
M.g = badHead @ Char
without prompting.
Nope, as far as I can tell "" gets translated to [], not unpackCString# "" - hence the unpack never gets in the way. If you had the second rule, you'd soon want the first.
So I wondered if I could write a rule for head/unpackCString
Urgh. not what we want though. GHC won't index the string at compile time, and I can't write a RULE for it.
Yeah, I tried that too...
Perhaps you can newtype Char and use string overloading to work around the packing issue?
That would work on GHC, but not on Hugs. Thanks Neil