Regular Expression Engine in 14 lines of Python

Re:Regular Expression Engine in 14 lines of Python by abecedarius on Sunday November 06, 2011 @12:21PM (#3203203)

In va(inp) or vb(inp) couldn't va(inp) succeed with an empty string as the result (at the end) which Python interprets as false, making it mistakenly try vb(x)? I haven't tried to run it.

Also I think c seems misleading as a variable name -- it suggests a single character, but the 'in c' means it's a set of characters.

[ Parent | on HN ]

Re:Regular Expression Engine in 14 lines of Python by 127 on Sunday November 06, 2011 @04:24PM (#3203888)

Yes, that is a bug and yes, those variable names do suck. Thanks for the correction.

    ordered_choice = lambda va,vb: lambda inp: (lambda a,b: a if a or a=="" else b)(va(inp),vb(inp))

Would work, but starts to be so ugly that I'd have to write proper functions and the code would not be 3 lines anymore. ;)

[ Parent | on HN ]

Re:Regular Expression Engine in 14 lines of Python by abecedarius on Sunday November 06, 2011 @06:30PM (#3204257)

How about

    eat = lambda chars: lambda s: s[1:] if s and s[0] in chars else None
    alt = lambda p, q: lambda s: (lambda r: q(s) if r is None else r)(p(s))
    seq = lambda p, q: lambda s: (lambda r: None if r is None else q(r))(p(s))

going a bit far in the short-names direction, oh well. :) It's too bad Python has this artificial statement/expression distinction.

[ Parent | on HN ]