| 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