xfst syntax (subset)

Commands

• source filename;
  Reads in a script file.
• read regex regular-expression;
  The regular expression may extend over multiple lines. It must be terminated with a semi-colon.
• define variable-name regular-expression;
  The regular expression may extend over multiple lines. It must be terminated with a semi-colon.
• apply up string
  Looks up the string using the top FST on the stack. If the string is in the lower language, you'll get the corresponding upper language strings back. If it's not in the lower language, you'll just get another xfst prompt.
• apply down string
  Analogously, but matching the string against the upper side language.
• print net
  Prints a description of the top network on the stack. In these descriptions, s indicates a non-final state, fs a final state. The start state is always numbered 0.

Regular expressions

• Square brackets delimit regular expressions.
• | indicates disjuction.
• A space indicates concatenation. The language [a b] consists of the single string "ab", which itself consists of two symbols, "a" and "b". The language [ab] also consists of the string "ab", but this time that string is only one symbol long. (It just happens to be a multi-character symbol.) Don't define multi-character symbols. Use the space.
• * is Kleene star.
• + is Kleene plus.
• : separates lower and upper tape.
• % is the escape character.
• ? is the wild card.
• () indicate optionality.
• \ indicates negation: \e is any single character other than e.
• ~ indicates language complement: ~[a] is the language of all strings other than the string "a".