gistfile1.txt

module Esolang
    open System
    open System.IO
    open FParsec
    open FParsec.CharParsers
    open FParsec.Primitives
    open FParsec.Error

    type Pattern =
        | As       of Pattern * Pattern
        | Seq      of Pattern * Pattern
        | Identity of string

    type Term =
        | List     of Expression list
        | Seq      of Expression * Expression 
        | Identity of string

    and Expression =
        | Production of Pattern * Expression
        | Term   of Term

    type Parser<'T> = Parser<'T,unit>

    let pExpressionList,pExpressionListImpl = createParserForwardedToRef()
    let pExpression,pExpressionImpl = createParserForwardedToRef()
    let pProduction,pProductionImpl = createParserForwardedToRef()
    let pPattern,pPatternImpl = createParserForwardedToRef()
    let pTerm,pTermImpl = createParserForwardedToRef()

    let pId : Parser<string> =
        many1Satisfy2L
        <| (fun x -> isLetter x || x = '_')
        <| (fun x -> isLetter x || isDigit x || x = '_')
        <| "identifier"

    do pExpressionListImpl :=
        pchar '{' >>. many pExpression .>> pchar '}'

    do pExpressionImpl :=
        pProduction <|>
        (pTerm |>> Expression.Term)

    do pProductionImpl :=
        ((pPattern .>> pchar '|' .>>. pProduction) |>> Expression.Production)

    do pPatternImpl :=
        (pipe3 pId (pchar ':') pPattern (fun x y z -> Pattern.As  (Pattern.Identity x,z))) <|>
        (pipe3 pId (pchar '.') pPattern (fun x y z -> Pattern.Seq (Pattern.Identity x,z))) <|>
        (pId |>> Pattern.Identity)

    do pTermImpl :=
        (pExpressionList |>> Term.List) <|>
        ((pExpression .>> pchar '.' .>>. pExpression) |>> Term.Seq ) <|>
        (pId |>> Term.Identity)