The question is similar to this one, but I want to parse an expression with function application using the OperatorPrecedenceParser
in FParsec
.
Here is my AST:
type Expression =
| Float of float
| Variable of VarIdentifier
| BinaryOperation of Operator * Expression * Expression
| FunctionCall of VarIdentifier (*fun name*) * Expression list (*arguments*)
I have the following input:
board→create_obstacle(4, 4, 450, 0, fric)
And here is the parser code:
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)))
My problem here is that the function arguments are expressions as well (they can include operators, variables etc) and I don't know how to extend my expr
parser to parse the argument list as a list of expression. I built a parser here, but I don't know how to combine it with my existing parser:
let primitive = expr <|> parenexpr
let argList = sepBy primitive (str_ws ",")
let fcall = tuple2 ident (between (str_ws "(") (str_ws ")") argList)
I currently have the following output from my parser:
Success: Expression (BinaryOperation
(Arrow,Variable "board",Variable "create_obstacle"))
What I want is to get the following:
Success: Expression
(BinaryOperation
(Arrow,
Variable "board",
Function (VarIdentifier "create_obstacle",
[Float 4, Float 4, Float 450, Float 0, Variable "fric"]))
You could parse the argument list as an optional postfix expression of an identifier
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))
and then define expr
like
let expr = (number |>> Float) <|> identWithOptArgs
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