如何使用FParsec解析带有多个参数的前缀函数(如Pow() )

Question

我尝试使用3+2，2解析前缀函数，比如Pow( FParsec )。我在示例文件中阅读了计算器教程，如下所示。这些例子都是一元前缀函数。我想知道如何使用FParsec.OperatorPrecedenceParser实现多个输入的前缀函数。

http://www.quanttec.com/fparsec/reference/operatorprecedenceparser.html#members.PrefixOperator

let number = pfloat .>> ws

let opp = new OperatorPrecedenceParser<float,unit,unit>()
let expr = opp.ExpressionParser
opp.TermParser <- number <|> between (str_ws "(") (str_ws ")") expr


opp.AddOperator(InfixOperator("+", ws, 1, Associativity.Left, (+)))
opp.AddOperator(InfixOperator("-", ws, 1, Associativity.Left, (-)))
opp.AddOperator(InfixOperator("*", ws, 2, Associativity.Left, (*)))
opp.AddOperator(InfixOperator("/", ws, 2, Associativity.Left, (/)))
opp.AddOperator(InfixOperator("^", ws, 3, Associativity.Right, fun x y -> System.Math.Pow(x, y)))
opp.AddOperator(PrefixOperator("-", ws, 4, true, fun x -> -x))

let ws1 = nextCharSatisfiesNot isLetter >>. ws
opp.AddOperator(PrefixOperator("log", ws1, 4, true, System.Math.Log))
opp.AddOperator(PrefixOperator("exp", ws1, 4, true, System.Math.Exp))

更新1

我按照字符串后解析器示例编写了一个快速脚本，因为我需要实际应用程序http://www.quanttec.com/fparsec/users-guide/tips-and-tricks.html#parsing-f-infix-operators的字符串后解析器。

abs(pow(1,2))可以被解析，但是pow(abs(1),2)不能被解析。我对如何使用前缀函数作为identWithArgs输入的一部分感到困惑。

#I @"..\packages\FParsec.1.0.2\lib\net40-client"
#r "FParsecCS.dll"
#r "FParsec.dll"

open FParsec

type PrefixFunc = POW
type Expr =
  | InfixOpExpr of string * Expr * Expr
  | PrefixOpExpr of string * Expr
  | PrefixFuncExpr of PrefixFunc * Expr list 
  | Number of int

let ws = spaces
let ws1 = spaces1
let str s = pstring s
let str_ws s = ws >>. str s .>> ws
let strci s = pstringCI s
let strci_ws s = ws >>. strci s .>> ws
let strciret_ws s x = ws >>. strci s .>> ws >>% x

let isSymbolicOperatorChar = isAnyOf "!%&*+-./<=>@^|~?"
let remainingOpChars_ws = manySatisfy isSymbolicOperatorChar .>> ws

let primitive = pint32 .>> ws |>> Number
let argList = sepBy primitive (str_ws ",")
let argListInParens = between (str_ws "(") (str_ws ")") argList
let prefixFunc = strciret_ws "pow" POW 
let identWithArgs =
    pipe2 prefixFunc argListInParens (fun funcId args -> PrefixFuncExpr(funcId, args))

let opp = new OperatorPrecedenceParser<Expr, string, unit>()
opp.TermParser <-
  primitive <|>
  identWithArgs <|>
  between (pstring "(") (pstring ")") opp.ExpressionParser

// a helper function for adding infix operators to opp
let addSymbolicInfixOperators prefix precedence associativity =
    let op = InfixOperator(prefix, remainingOpChars_ws,
                           precedence, associativity, (),
                           fun remOpChars expr1 expr2 ->
                               InfixOpExpr(prefix + remOpChars, expr1, expr2))
    opp.AddOperator(op)

// the operator definitions:
addSymbolicInfixOperators "*"  10 Associativity.Left
addSymbolicInfixOperators "**" 20 Associativity.Right

opp.AddOperator(PrefixOperator("abs",remainingOpChars_ws,3,true,(),fun remOpChars expr -> PrefixOpExpr("abs", expr)))
opp.AddOperator(PrefixOperator("log",remainingOpChars_ws,3,true,(),fun remOpChars expr -> PrefixOpExpr("log", expr)))

run opp.ExpressionParser "abs(pow(1,2))"
run opp.ExpressionParser "pow(abs(1),2)"

Answer 1

一年后，我开始重新审视这个问题，终于意识到了这个问题。

我已经更改了以下代码

let argList = sepBy primitive (str_ws ",")

到以下

let opp = new OperatorPrecedenceParser<Expr, string, unit>()
let argList = sepBy opp.ExpressionParser (str_ws ",")

我把OperatorPrecedenceParser带到了代码的开头。然后，通过将opp.ExpressionParser直接放入argList中，实现递归调用它。

我刚刚意识到OperatorPrecedenceParser与createParserForwardedToRef非常相似。它首先创建一个解析器，然后再编写实现。FParsec必须以这种方式实现递归。类似于它的JSON示例解析器。

在此改变之后，可以解析abs(pow(1,2))和pow(abs(1),2)。希望这能帮助其他曾经遇到这个问题的人。