haskell - Why is there a limit on the length of a regex pattern in Text.Regex.Posix? -

i'm seeing odd arbitrary limit on length of regular expression pattern where, after string of 30 characters, funny things start happen.

simple ghci example:

> import text.regex.posix > "abcdefghijklmnopqrstuvwxyz0123456789" =~ "abcdefghijklmnopqrstuvwxyz0123" :: string "abcdefghijklmnopqrstuvwxyz0123" > "abcdefghijklmnopqrstuvwxyz0123456789" =~ "abcdefghijklmnopqrstuvwxyz01234" :: string "" 

the difference addition of 4 @ end of last pattern. it's valid regex , should match gives me empty string.

it gets weirder if add few more valid characters pattern:

> "abcdefghijklmnopqrstuvwxyz0123456789" =~ "abcdefghijklmnopqrstuvwxyz01234567" :: string "ab" 

it tells me matches ab when that's wrong.

my environment:

• stack version 1.1.2 (resolver lts-6.7)
• ghc version 7.10.3
• os: windows 10
• regex-posix-0.95.2

a complete uninstall , reinstall of stack , packages did not solve problem

following this discussion, seems there other issues library stemming underlying c code not being ported 64-bit architecture.

i have switched regex-tdfa package , no longer have these problems.