AjayMT / kenfa

regular expressions with thompson's algorithm

kenfa

Kenfa ("Ken F A") is a regular expression tool+library based on Thompson's algorithm and this excellent article by Russ Cox.

Kenfa currently supports the following operators:

• *: zero or more matched strings (ex: a* matches "", "a", "aa", ...)
• +: one or more matched strings (ex: a+ matches "a", "aa", "aaa", ...)
• ?: zero or one matched strings (ex: a? matches "", "a")
• |: alternation / union; this operator has lower precedence than concatenation (ex: ab|cd matches "ab", "cd")
• (): grouping (ex: "a(b|c)d" matches "abd", "acd")

Operators can be escaped with a backslash: \* matches a literal * character.

Kenfa can match regular expressions against strings and can produce DOT diagrams of the DFAs it creates when compiling regular expressions.

Build

You will need:

• the OCaml toolchain
• the dune build system

dune build
dune install

Usage

kenfa <regexp> <input>
kenfa -d <regexp> [<input>]

Options:
  -d 	Output the generated DFA as a DOT diagram.
  -help  Display this list of options
  --help  Display this list of options

Kenfa will match the given regular expression against the input and output true or false. When the -d flag is provided, it outputs a DOT diagram:

$ kenfa -d "a(b|c)d+"
digraph DFA {
3 -> 3 [ label="d" ];
2 -> 3 [ label="d" ];
1 -> 2 [ label="c" ];
1 -> 2 [ label="b" ];
0 -> 1 [ label="a" ];
3 [ peripheries=2 ];
}

Compiling the DOT diagram with dot -Tsvg -O produces the following SVG: