anagrep: Find strings with permutations (anagrams) that match a regular expression

A Haskell library for matching permutations of regular expressions: http://hackage.haskell.org/package/anagrep

And a command-line interface, useful for puzzle solving (e.g., which English word has one 'p', one 'q', and four vowels?):

Usage: anagrep REGEXP [FILE]...
Print lines in each FILE (or stdin) for which some permutation (anagram)
matches the given REGEXP.  REGEXP is a restricted regular expression that can
contain the following patterns:
  Character matches
    x         single literal character
    [aein-z]  character set (any listed character)
    [^a-mou]  negated character set (any character not listed)
    .         any single character
    \x        escape single literal character (no special meanings)
  Repeat modifiers - may only be applied to characters (above)
    {N,M}     repeat character N-M times
    {N,}      repeat character at least N times
    {N}       equivalent to {N,N}
    ?         equivalent to {0,1}
    *         equivalent to {0,}
    +         equivalent to {1,}
  Combination
    XY        concatenation matches pattern X and Y in either order
    X|Y       alternation matches pattern X or Y
    (X)       grouping (only useful for alternation - note that successive
              grouped alternations involve a cross-product expansion and may
              be slow)
Other regular expression features are not currently supported.  Matching is
always done on entire lines (like grep -x).

Example: anagrep 'pq[aeiou]{4}' /usr/share/dict/words
  > opaque

Flags:
  -b    treat input as raw byte sequence (uses locale encoding by default)
  -i    ignore case distinctions in patterns and data