RegEx Syntax

We currently use a very simplified form for regular expression syntax.

Operators:

• A match of α|β consists of either a match of α or a match of β
• A match of αβ consists of a match of α followed by a match of β
• A match of α? consists of at most one match of α
• A match of α* consists of zero or more back-to-back matches of α
• A match of α+ consists of one or more back-to-back matches of α
• A match of α{m} consists of exactly m back-to-back matches of α
• A match of α{m,n} consists of at least m but at most n back-to-back matches of α
• A match of α{m,} consists of m or more back-to-back matches of α
• A match of α{,n} consists of at most n back-to-back matches of α
• A match of (α) consists of a match of α

These are listed from lowest to highest precedence.

Character matching:

• . matches any character.
• A single character matches itself with the exception of the special characters: ., ?, *, +, |, \, (, ), {, }, [, ]. These special characters can be matched by preceding them with an escape character \.
• [c] matches one character from the class c.
• [^c] matches one character not in the class c.

Character classes support single characters and character ranges. The special characters -, [, \, ] must be preceded by an escape character \ within a class.

def Parser.RegEx.compile? (s : String) : Option (RegEx Char)

Compiles a regex from a string, returns none on faiure

Equations

• Parser.RegEx.compile? s = match (Parser.RegEx.re0✝ <* Parser.endOfInput).run s.toSubstring with | Parser.Result.ok a r => some r | Parser.Result.error a a_1 => none

def Parser.RegEx.compile! (s : String) : RegEx Char

Compiles a regex from a string, panics on faiure

Equations

• Parser.RegEx.compile! s = match Parser.RegEx.compile? s with | some r => r | none => panicWithPosWithDecl "Parser.RegEx.Compile" "Parser.RegEx.compile!" 179 12 "invalid regular expression"