| I could imagine adding two rules to the simplifier:
|
| case unpackCString# "" of ==> case [] of
| case unpackCString# "xyz" of ==> case (C# 'x': unpackCString# "yz") of
...
| This goes back to an old gripe of mine actually -- we can't get
| at the length of a C string literal at compile time either, which
| would be super useful in rules.
|
| If we had some light primitives for this, that GHC new about (head#,
| length#), that accessed the internal data about what strings are up to,
| that could be useful.
Don, Neil
Can you two be very concrete about what you'd like? This stuff is very like
constant folding. GHC knows about
1# +# 2#
so it could reasonably know about
length# "foo"
where
length# :: CString -> Int
or whatever.
Both Neil's suggestion and the above look do-able. But I'd like a clear spec
first. There is a slight tension between what is "built-in magic" for
primitive types (in this case CString), and what is general purpose stuff. I
don't think there is anything wrong with magic for primitive types, but if
there is a useful general-purpose mechanism trying to get out, let's liberate
it.
Simon
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