Parser.elm

module Parser exposing (..)

import Combine exposing (..)
import Combine.Char exposing (char)
import Combine.Num exposing (int)


type Program
    = Program Expr


type Expr
    = NumOp Expr OpType Expr
    | NumLiteral Int


type OpType
    = Add
    | Sub
    | Div


program : Parser s Program
program =
    Program <$> expr <* end


expr : Parser s Expr
expr =
    let
        helper =
            choice
                [ numOp
                , numLiteral
                ]
    in
        whitespace *> helper <* whitespace


numOp : Parser s Expr
numOp =
    lazy <|
        \() ->
            succeed NumOp
                <*> numLiteral
                <* whitespace
                <*> opType
                <* whitespace
                <*> expr


opType : Parser s OpType
opType =
    choice
        [ Add <$ char '+'
        , Sub <$ char '-'
        , Div <$ char '/'
        ]


numLiteral : Parser s Expr
numLiteral =
    NumLiteral <$> int