open FParsec

​

type Expression =

    | Identifier of string

    | Call of string * Expression list

    | And of Expression * Expression

    | Or of Expression * Expression

​

let identifier = many1Satisfy isLetter

​

let expr, exprRef = createParserForwardedToRef()

​

let callExpr = 

    pipe2 

        (identifier .>> spaces .>> pchar '(' .>> spaces) 

        (sepBy expr (pchar ',' .>> spaces)) 

        (fun name args -> Call(name, args))

​

let atomExpr = 

    choice [

        callExpr;

        identifier |>> Identifier;

        between (pchar '(' .>> spaces) (pchar ')' .>> spaces) expr

    ]

​

let opp = new OperatorPrecedenceParser<Expression, unit, unit>()

​

opp.AddOperator(InfixOperator("|", spaces, 10, Associativity.Left, fun l r -> Or(l, r)))

opp.AddOperator(InfixOperator("&", spaces, 20, Associativity.Left, fun l r -> And(l, r)))

​

exprRef.Value <- attempt atomExpr <|> opp.ExpressionParser

​

run expr "(A & B) | F(C)"

|> printfn "%A"

​

// Expected: Or (And (Identifier "A", Identifier "B"), Call ("F", [Identifier "C"]))