Weyland

Weyland provides an alternative way to write regular expression handling incomplete matching and lexers using them.

Install with: pip install weyland

A. Syntax of regular expression

Weyland offers three classes: Regex for regexes, Match for matches and Element.

A Regex is composed of Elements.

Below is a short definition of the language used to define Regex.

A.1 Sequence

ab a then b

A.2 Classes

A class is a group of characters represented by a single special character.

• # or \d any digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
• @ or \a any letters
• & or \w any digits, letters and the underscore character (_)
• . any characters which is not a new line

A.3 Positions

A position can be also represented by a single special character.

• ^ start of the string (can be used only at the start of the Regex)
• $ end of the string (can be used only at the end of the Regex)

A.4 Choices

[ab] a or b

A.5 Optionality and repetition

Optionality and repetition of a character, a class or a choice can be represented by a single special character.

• a?b b or ab (a is optionnal, it can appear between 0 and 1 time),
• a+b ab, aab, aaab, aaaab, etc. (a is mandatory, it must appear betweean 1 and X times),
• a*b b, ab, aab, aaab, aaaab, etc. (a is optionnal, it can appear between 0 and X times).

Optionality and repetition can't be used for positions.

A.6 Escaping special characters

In order to use a special characters as a normal character in a regex, you must escape them by putting the () character before it.

There are 12 escapable characters: #, @, &, ., ^, $, [, ], ?, +, *, .

A.7 Limitations

• In a choice, you can only choose between one element not between sequences,
• In a choice, no repeated element nor optionnal element.
• In a choice, no start nor end of the string elements.
• You can only use terminals and special characters in regex definitions.
• You can't define groups in regex definitions.

B. Lexers

Weyland provides also several lexers using the incomplete matching feature of Weyland's regex.

B.1 Languages available

A set of lexers and associated tokens are available for the following languages:

• Data language: json,
• Programming languages: ash, lua, python,
• Description languages: bnf, hamill.

C. Websites

List of websites about Weyland:

• Source code on Github: https://github.com/Xitog/weyland
• Project on PyPI: https://pypi.org/project/weyland/
• Documentation: see project description on Github or PyPI
• Stats: https://libraries.io/pypi/weyland