peg-3-parseExpression.fs

let parseExpression (grammar:Map<string,GrammarRule<'a>>) start (input:string) =
    let rec parse offset = function
    | Terminal x -> 
        let e = offset + x.Length - 1
        if e < input.Length && input.[offset..e] = x then (TerminalSymbol x, e + 1) else (Unmatched, offset)
    | TerminalOneOf x -> match currentCharacter input offset with
                         | Some c -> if x.Contains(c) then (TerminalSymbol c, offset + c.Length) else (Unmatched, offset)
                         | None -> (Unmatched, offset)
    | TerminalWildcard -> match currentCharacter input offset with 
                          | Some c -> (TerminalSymbol c, offset + c.Length)
                          | None -> (Unmatched, offset)
    | TerminalUnicode x -> match currentCharacter input offset with
                           | Some c -> if Char.GetUnicodeCategory(c, 0) = x then (TerminalSymbol c, offset + c.Length) else (Unmatched, offset)
                           | None -> (Unmatched, offset)
    | NonTerminal x -> 
        let rule = grammar.[x]
// .
// .