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Parsing function application with FParsec using OperatorPrecedenceParser?
type Expression =
  | Float of float
  | Variable of VarIdentifier
  | BinaryOperation of Operator * Expression * Expression
  | FunctionCall of VarIdentifier (*fun name*) * Expression list (*arguments*)

board→create_obstacle(4, 4, 450, 0, fric)

let expr = (number |>> Float) <|> (ident |>> Variable)
let parenexpr = between (str_ws "(") (str_ws ")") expr

let opp = new OperatorPrecedenceParser<_,_,_>()

opp.TermParser <- expr <|> parenexpr

opp.AddOperator(InfixOperator("→", ws,
  10, Associativity.Right,
  fun left right -> BinaryOperation(Arrow, left, right)))

let primitive = expr <|> parenexpr
let argList = sepBy primitive (str_ws ",")
let fcall = tuple2 ident (between (str_ws "(") (str_ws ")") argList)

Success: Expression (BinaryOperation
     (Arrow,Variable "board",Variable "create_obstacle"))

Success: Expression
      (BinaryOperation
            (Arrow,
                Variable "board",
                Function (VarIdentifier "create_obstacle",
                          [Float 4, Float 4, Float 450, Float 0, Variable "fric"]))

let argListInParens = between (str_ws "(") (str_ws ")") argList
let identWithOptArgs =
    pipe2 ident (opt argListInParens)
          (fun id optArgs -> match optArgs with
                             | Some args -> FunctionCall(id, args)
                             | None -> Variable(id))

let expr = (number |>> Float) <|> identWithOptArgs