Re: [Pyparsing] multiple tokens but no repeats

[Ralph C. <ra...@in...>]

Hi Tim,

> I'm trying to represent the logic that I wish to match 0 or more
> tokens, up to a maximum of 4 tokens, but I don't want any repeats of
> tokens already matched within the group of 4. How could I do that?

I'm not sure if you can.  Perhaps there's a way to run your own
validation code as each attempt to grow the number of matches occurs?

Otherwise, since there's only four I'd enumerate the alternatives, e.g.

    a
    ab   ac   ad
    abc  abd  acb  acd  adb  adc
    abcd abdc acbd acdb adbc adcb

If I've got that right, there's 16 alternatives starting with `a'.  The
other three follow a similar pattern making 64 in total.  You could
factor out the common prefixes to speed up a Regex() a bit if you find
that just a dumb list seems slow.  Be sure to check whether order
determines whether it matches the longest possible, e.g. `abcz' should
match `abc' and not `a' or `ab'.

Cheers,


Ralph.