Created
February 1, 2013 08:18
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| let checkForLeftRecursion (rules:Map<string,Expression>) = | |
| let rec leftRules = function | |
| | Terminal _ | TerminalOneOf _ | TerminalUnicode _ | TerminalWildcard | Epsilon -> [] | |
| | NonTerminal x -> [x] | |
| | ZeroOrMore x | OneOrMore x | Optional x | Not x | And x -> leftRules x | |
| | Choice x -> | |
| List.concat <| List.map leftRules x | |
| | Sequence x -> | |
| let rec processList = function | |
| | [] -> [] | |
| | (head :: tail) -> | |
| match head with | |
| | Optional _ | Not _ | And _ | ZeroOrMore _ | OneOrMore _ -> List.append (leftRules head) (processList tail) | |
| | x -> leftRules head | |
| processList x | |
| | Rule _ -> failwith "Internal error" | |
| let rec checkRule name prior = | |
| if List.exists ((=) name) prior then | |
| failwithf "Left recursion calling %s" <| List.reduce (fun a b -> (b + " -> " + a)) (name :: prior) | |
| match Map.tryFind name rules with | |
| | None -> failwithf "Unknown rule %s" name | |
| | Some x -> | |
| let leftchoices = leftRules x | |
| let sp = (name :: prior) | |
| for rule in leftchoices do checkRule rule sp done | |
| try | |
| Map.iter (fun k _ -> checkRule k []) rules | |
| with | |
| | ex -> eprintfn "Grammar error: %s" ex.Message | |
| failwith "Invalid Grammar" |
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