OK, it turns out that having [^\x00] as a character range gives me the error with pred. [\x00] works fine; [^\x00] gives the error message. On Sat, Mar 24, 2012 at 6:33 PM, Omari Norman wrote:

I'm wrinting (or at least, trying to write) an Alex lexer. Say I want to group character ranges together and specify that I want a character that is *not* in any of those ranges. Example

---

{ module Main where }

%wrapper "posn-bytestring"

$lowAscii = \x00-\x1f -- unprintable stuff $lowSymbol = \x21-\x2f -- exclamation point to solidus $space = \x20

$special = [^$lowAscii $lowSymbol]

lex :-

$special { Word }

{ data Token = Word AlexPosn ByteString.ByteString }

When I run this through Alex, I get "Prelude.Enum.Char.pred: bad argument".

What am I doing wrong? How would I accomplish this sort of thing? Thanks. --Omari