FParsec 的缩进、表达式、语句和 StackOverflowException - 错误
Indentation, expressions, statements and StackOverflowException with FParsec - Errors
根据 this implementation，我使用 FParsec 测试缩进，但是当我通过添加表达式（文字、列表、元组和算术运算）使其变得更复杂时，允许表达式到顶层，并且添加变量创建语句；我首先收到 WhosebugException 错误。在我看来，这是因为表达式解析器以在程序中形成无限循环的方式请求。我看不出其他原因，但是，我不知道如何解决这个问题。
如果我从我的解析器数据 statement 中删除 attempt pexpression，则不再有 WhosebugException，但是模块 IndentationParserWithoutBacktracking（因此管理缩进）告诉我要解析的代码缺少 "newline":
Failure: Error in Ln: 2 Col: 1
loop i 0 10
^
Expecting: let or print
The parser backtracked after:
Error in Ln: 3 Col: 5
let myVar = 2 + 1
^
Expecting: loop or print
The parser backtracked after:
Error in Ln: 3 Col: 17
let myVar = 2 + 1
^
Expecting: newline
这一切都根据下面的文字来解析：
loop i 0 10
let myVar = 2 + 1
print myVar
这是我的代码：
open FParsec
// module IndentationParserWithoutBacktracking // see the link
// Utils
open IndentationParserWithoutBacktracking
let isBlank = fun c -> c = ' ' || c = '\t'
let ws = spaces
let ws1 = skipMany1SatisfyL isBlank "whitespace"
let str s = pstring s .>> ws
let keyword str = pstring str >>? nextCharSatisfiesNot (fun c -> isLetter c || isDigit c) <?> str
// AST
type Identifier = Identifier of string
type InfixOp =
| Sum | Sub | Mul | Div | Pow | Mod
| And | Or | Equal | NotEqual | Greater | Smaller | GreaterEqual | SmallerEqual
type Value =
| Int of int
| Float of float
| Bool of bool
| String of string
| Char of char
| Variable of Identifier
type Expr =
| Literal of Value
| Infix of Expr * InfixOp * Expr
| List of Expr list
| Tuple of Expr list
type Statement =
| Expression of Expr
| Let of Identifier * Statement list
| Loop of Identifier * Expr * Expr * Statement list
| Print of Identifier
// Literals
let numberFormat = NumberLiteralOptions.AllowMinusSign ||| NumberLiteralOptions.AllowFraction |||
NumberLiteralOptions.AllowHexadecimal ||| NumberLiteralOptions.AllowOctal |||
NumberLiteralOptions.AllowBinary ||| NumberLiteralOptions.AllowPlusSign
let literal_numeric =
numberLiteral numberFormat "number" |>> fun nl ->
if nl.IsInteger then Literal (Int(int nl.String))
else Literal (Float(float nl.String))
let literal_bool =
(choice [
(stringReturn "true" (Literal (Bool true)))
(stringReturn "false" (Literal (Bool false)))
]
.>> ws) <?> "boolean"
let literal_string =
(between (pstring "\"") (pstring "\"") (manyChars (satisfy (fun c -> c <> '"')))
|>> fun s -> Literal (String s)) <?> "string"
let literal_char =
(between (pstring "'") (pstring "'") (satisfy (fun c -> c <> '''))
|>> fun c -> Literal (Char c)) <?> "character"
let identifier =
(many1Satisfy2L isLetter (fun c -> isLetter c || isDigit c) "identifier"
|>> fun i -> Identifier i) <?> "valid identifier"
let betweenParentheses p =
(between (str "(") (str ")") p)
let variable = identifier |>> fun id -> Literal (Variable id)
let literal = (attempt literal_numeric <|>
attempt literal_bool <|>
attempt literal_char <|>
attempt literal_string <|>
attempt variable) <?> "literal"
// Expressions
let pexpr, pexprimpl = createParserForwardedToRef()
let term =
(ws >>. literal .>> ws) <|>
(betweenParentheses (ws >>. pexpr)) <|>
(ws >>. pexpr .>> ws)
let infixOperator (p: OperatorPrecedenceParser<_, _, _>) op prec map =
p.AddOperator(InfixOperator(op, ws, prec, Associativity.Left, map))
let ops =
// Arithmetic
[ "+"; "-"; "*"; "/"; "%" ] @
// Logical
[ "&&"; "||"; "=="; "!="; ">"; "<"; ">="; "<=" ]
let opCorrespondance op =
match op with
// Arithmetic operators
| "+" -> Sum
| "-" -> Sub
| "*" -> Mul
| "/" -> Div
| "%" -> Mod
// Logical operators
| "&&" -> And
| "||" -> Or
| "==" -> Equal
| "!=" -> NotEqual
| ">" -> Greater
| "<" -> Smaller
| ">=" -> GreaterEqual
| "<=" -> SmallerEqual
let opParser = new OperatorPrecedenceParser<_, _, _>()
for op in ops do
infixOperator opParser op 1 (fun x y -> Infix(x, opCorrespondance op, y))
opParser.TermParser <- term
let list = between (str "[") (str "]") (sepBy pexpr (str ",")) |>> List
let tuple = between (str "(") (str ")") (sepBy pexpr (str ",")) |>> Tuple
let expression =
opParser.ExpressionParser <|> // I removed this line to don't have the mistake again.
list <|>
tuple <|>
literal
pexprimpl := attempt expression
// Statements
let statements, statementsRef = createParserForwardedToRef()
let pexpression = expression |>> Expression
let plet =
pipe2
(keyword "let" >>. ws1 >>. identifier)
(ws >>. str "=" >>. ws >>. statements)
(fun id gtt exp -> Let(id, gtt, exp))
// From the link, but "revisited"
let ploop =
pipe4
(keyword "loop" >>. ws1 >>. identifier)
(ws1 >>. literal) // If I put 'pexpr', it doesn't work too...
(ws1 >>. literal)
(statements)
(fun id min max stmts -> Loop(id, min, max, stmts))
let print = keyword "print" >>. (ws1 >>. identifier |>> Print)
let statement =
attempt plet <|>
attempt print <|>
attempt ploop <|>
attempt pexpression
statementsRef := indentedMany1 statement "statement"
let document = statements .>> spaces .>> eof
let test str =
match runParserOnString document (UserState.Create()) "" str with
| Success(result, _, _) -> printfn "Success: %A" result
| Failure(errorMsg, _, _) -> printfn "Failure: %s" errorMsg
System.Console.Clear()
test @"
loop i 0 10
let myVar = 2 + 1
print myVar
"
我知道我同时问了好几个问题，而且网站确实不允许，但它们都有点联系在一起，所以我还不如一石二鸟...
我真的很想了解我的错误，以便为非常小的 ML-like 语言设计一个解析器。
谢谢。
编辑
这是我当前的代码，已修改以响应遇到的第一个缩进问题：
open IndentationParserWithoutBacktracking // So from the link
let isBlank = fun c -> c = ' ' || c = '\t'
let ws = spaces
let ws1 = skipMany1SatisfyL isBlank "whitespace"
let str s = pstring s .>> ws
let keyword str = pstring str >>? nextCharSatisfiesNot (fun c -> isLetter c || isDigit c) <?> str
// AST
type Identifier = Identifier of string
type Value =
| Int of int
| Float of float
| Bool of bool
| String of string
| Char of char
| Variable of Identifier
// In FP, "all" is an expression, so:
type Expr =
// Arithmetic + lists and tuple
| Literal of Value
| Infix of Expr * InfixOp * Expr
| List of Expr list
| Tuple of Expr list
// Statements
| Return of Expr
| Loop of Identifier * Expr * Expr * Expr list
| Print of Identifier
and InfixOp =
| Sum | Sub | Mul | Div | Pow | Mod
| And | Or | Equal | NotEqual | Greater | Smaller | GreaterEqual | SmallerEqual
// Literals
let numberFormat = NumberLiteralOptions.AllowMinusSign ||| NumberLiteralOptions.AllowFraction |||
NumberLiteralOptions.AllowHexadecimal ||| NumberLiteralOptions.AllowOctal |||
NumberLiteralOptions.AllowBinary
let literal_numeric =
numberLiteral numberFormat "number" |>> fun nl ->
if nl.IsInteger then Literal (Int(int nl.String))
else Literal (Float(float nl.String))
let literal_bool =
(choice [
(stringReturn "true" (Literal (Bool true)))
(stringReturn "false" (Literal (Bool false)))
]
.>> ws) <?> "boolean"
let literal_string =
(between (pstring "\"") (pstring "\"") (manyChars (satisfy (fun c -> c <> '"')))
|>> fun s -> Literal (String s)) <?> "string"
let literal_char =
(between (pstring "'") (pstring "'") (satisfy (fun c -> c <> '''))
|>> fun c -> Literal (Char c)) <?> "character"
let identifier =
(many1Satisfy2L isLetter (fun c -> isLetter c || isDigit c) "identifier"
|>> fun i -> Identifier i) <?> "identifier"
let betweenParentheses p =
(between (str "(") (str ")") p) <?> ""
let variable = identifier |>> fun id -> Literal (Variable id)
let literal = (attempt literal_numeric <|>
attempt literal_bool <|>
attempt literal_char <|>
attempt literal_string <|>
attempt variable) <?> "literal"
// Expressions and statements
let pexprs, pexprimpl = createParserForwardedToRef()
// `ploop` is located here to force `pexprs` to be of the type `Expr list`, `ploop` requesting an expression list.
let ploop =
pipe4
(keyword "loop" >>. ws1 >>. identifier)
(ws1 >>. literal)
(ws1 >>. literal)
(pexprs)
(fun id min max stmts -> Loop(id, min, max, stmts))
// `singlepexpr` allows to use only one expression.
let singlepexpr =
pexprs |>> fun ex -> ex.Head
let term =
(ws >>. singlepexpr .>> ws) <|>
(betweenParentheses (ws >>. singlepexpr)) <|>
(ws >>. literal .>> ws) <|>
(betweenParentheses (ws >>. literal))
let infixOperator (p: OperatorPrecedenceParser<_, _, _>) op prec map =
p.AddOperator(InfixOperator(op, ws, prec, Associativity.Left, map))
let ops =
// Arithmetic
[ "+"; "-"; "*"; "/"; "%" ] @
// Logical
[ "&&"; "||"; "=="; "!="; ">"; "<"; ">="; "<=" ]
let opCorrespondance op =
match op with
// Arithmetic operators
| "+" -> Sum
| "-" -> Sub
| "*" -> Mul
| "/" -> Div
| "%" -> Mod
// Logical operators
| "&&" -> And
| "||" -> Or
| "==" -> Equal
| "!=" -> NotEqual
| ">" -> Greater
| "<" -> Smaller
| ">=" -> GreaterEqual
| "<=" -> SmallerEqual
let opParser = new OperatorPrecedenceParser<Expr, unit, UserState>()
for op in ops do
infixOperator opParser op 1 (fun x y -> Infix(x, opCorrespondance op, y))
opParser.TermParser <- term
let list = (between (str "[") (str "]") (sepBy singlepexpr (str ",")) |>> List) <?> "list"
let tuple = (between (str "(") (str ")") (sepBy singlepexpr (str ",")) |>> Tuple) <?> "tuple"
// Statements
// A commented `let` expression, commented for tests with the `return` instruction.
//let plet =
// pipe3
// (keyword "let" >>. ws1 >>. identifier)
// (ws >>. gtt ":")
// (ws >>. str "=" >>. ws >>. pexprs)
// (fun id gtt exp -> Let(id, gtt, exp))
let preturn =
keyword "return" >>. ws >>. singlepexpr
|>> fun ex -> Return ex
let print = keyword "print" >>. (ws1 >>. identifier |>> Print)
let instruction =
print <|>
ploop <|>
preturn <|>
opParser.ExpressionParser <|> // So we add the arithmetic, like x + y or 21 * 32 - 12 for example
list <|>
tuple <|>
literal
pexprimpl := indentedMany1 instruction "instruction"
let document = pexprs .>> spaces .>> eof
let test str =
match runParserOnString document (UserState.Create()) "" str with
| Success(result, _, _) -> printfn "%A" result
| Failure(errorMsg, _, _) -> printfn "%s" errorMsg
System.Console.Clear()
// The test code that give an error of "newline" expecting
let code = test @"
return 2 + 1
"
这里有一些关于错误的截图：
为什么 indentedMany1 告诉你它在你的示例代码中期待一个换行符是因为它正在寻找：一个缩进的 块 。不是一行中的一个表达式。所以你的 let myVar = 2 + 1 行混淆了它。如果你写成：
let myVar =
2 + 1
那我打赌它会起作用。
我相信，您需要的是更改 let 解析器以允许以下两种情况之一：或者 单行表达式， 或 语句块（您的 statements 解析器）。即，类似于：
let pLetValue = expression <|> statements
let plet =
pipe2
(keyword "let" >>. ws1 >>. identifier)
(ws >>. str "=" >>. ws >>. pLetValue)
(fun id gtt exp -> Let(id, gtt, exp))
请注意，我还没有对此进行测试，因为我今天没有太多时间。您可能需要 attempt expression（或 pexpr，两者是一回事），而不是上面的 expression。稍微试验一下，看看会发生什么；如果您在尝试弄清楚 FParsec 如何处理给定表达式时完全迷失了方向，请记住 http://www.quanttec.com/fparsec/users-guide/debugging-a-parser.html.
中给出的建议
根据 this implementation，我使用 FParsec 测试缩进，但是当我通过添加表达式（文字、列表、元组和算术运算）使其变得更复杂时，允许表达式到顶层，并且添加变量创建语句；我首先收到 WhosebugException 错误。在我看来，这是因为表达式解析器以在程序中形成无限循环的方式请求。我看不出其他原因，但是，我不知道如何解决这个问题。
如果我从我的解析器数据 statement 中删除 attempt pexpression，则不再有 WhosebugException，但是模块 IndentationParserWithoutBacktracking（因此管理缩进）告诉我要解析的代码缺少 "newline":
Failure: Error in Ln: 2 Col: 1
loop i 0 10
^
Expecting: let or print
The parser backtracked after:
Error in Ln: 3 Col: 5
let myVar = 2 + 1
^
Expecting: loop or print
The parser backtracked after:
Error in Ln: 3 Col: 17
let myVar = 2 + 1
^
Expecting: newline
这一切都根据下面的文字来解析：
loop i 0 10
let myVar = 2 + 1
print myVar
这是我的代码：
open FParsec
// module IndentationParserWithoutBacktracking // see the link
// Utils
open IndentationParserWithoutBacktracking
let isBlank = fun c -> c = ' ' || c = '\t'
let ws = spaces
let ws1 = skipMany1SatisfyL isBlank "whitespace"
let str s = pstring s .>> ws
let keyword str = pstring str >>? nextCharSatisfiesNot (fun c -> isLetter c || isDigit c) <?> str
// AST
type Identifier = Identifier of string
type InfixOp =
| Sum | Sub | Mul | Div | Pow | Mod
| And | Or | Equal | NotEqual | Greater | Smaller | GreaterEqual | SmallerEqual
type Value =
| Int of int
| Float of float
| Bool of bool
| String of string
| Char of char
| Variable of Identifier
type Expr =
| Literal of Value
| Infix of Expr * InfixOp * Expr
| List of Expr list
| Tuple of Expr list
type Statement =
| Expression of Expr
| Let of Identifier * Statement list
| Loop of Identifier * Expr * Expr * Statement list
| Print of Identifier
// Literals
let numberFormat = NumberLiteralOptions.AllowMinusSign ||| NumberLiteralOptions.AllowFraction |||
NumberLiteralOptions.AllowHexadecimal ||| NumberLiteralOptions.AllowOctal |||
NumberLiteralOptions.AllowBinary ||| NumberLiteralOptions.AllowPlusSign
let literal_numeric =
numberLiteral numberFormat "number" |>> fun nl ->
if nl.IsInteger then Literal (Int(int nl.String))
else Literal (Float(float nl.String))
let literal_bool =
(choice [
(stringReturn "true" (Literal (Bool true)))
(stringReturn "false" (Literal (Bool false)))
]
.>> ws) <?> "boolean"
let literal_string =
(between (pstring "\"") (pstring "\"") (manyChars (satisfy (fun c -> c <> '"')))
|>> fun s -> Literal (String s)) <?> "string"
let literal_char =
(between (pstring "'") (pstring "'") (satisfy (fun c -> c <> '''))
|>> fun c -> Literal (Char c)) <?> "character"
let identifier =
(many1Satisfy2L isLetter (fun c -> isLetter c || isDigit c) "identifier"
|>> fun i -> Identifier i) <?> "valid identifier"
let betweenParentheses p =
(between (str "(") (str ")") p)
let variable = identifier |>> fun id -> Literal (Variable id)
let literal = (attempt literal_numeric <|>
attempt literal_bool <|>
attempt literal_char <|>
attempt literal_string <|>
attempt variable) <?> "literal"
// Expressions
let pexpr, pexprimpl = createParserForwardedToRef()
let term =
(ws >>. literal .>> ws) <|>
(betweenParentheses (ws >>. pexpr)) <|>
(ws >>. pexpr .>> ws)
let infixOperator (p: OperatorPrecedenceParser<_, _, _>) op prec map =
p.AddOperator(InfixOperator(op, ws, prec, Associativity.Left, map))
let ops =
// Arithmetic
[ "+"; "-"; "*"; "/"; "%" ] @
// Logical
[ "&&"; "||"; "=="; "!="; ">"; "<"; ">="; "<=" ]
let opCorrespondance op =
match op with
// Arithmetic operators
| "+" -> Sum
| "-" -> Sub
| "*" -> Mul
| "/" -> Div
| "%" -> Mod
// Logical operators
| "&&" -> And
| "||" -> Or
| "==" -> Equal
| "!=" -> NotEqual
| ">" -> Greater
| "<" -> Smaller
| ">=" -> GreaterEqual
| "<=" -> SmallerEqual
let opParser = new OperatorPrecedenceParser<_, _, _>()
for op in ops do
infixOperator opParser op 1 (fun x y -> Infix(x, opCorrespondance op, y))
opParser.TermParser <- term
let list = between (str "[") (str "]") (sepBy pexpr (str ",")) |>> List
let tuple = between (str "(") (str ")") (sepBy pexpr (str ",")) |>> Tuple
let expression =
opParser.ExpressionParser <|> // I removed this line to don't have the mistake again.
list <|>
tuple <|>
literal
pexprimpl := attempt expression
// Statements
let statements, statementsRef = createParserForwardedToRef()
let pexpression = expression |>> Expression
let plet =
pipe2
(keyword "let" >>. ws1 >>. identifier)
(ws >>. str "=" >>. ws >>. statements)
(fun id gtt exp -> Let(id, gtt, exp))
// From the link, but "revisited"
let ploop =
pipe4
(keyword "loop" >>. ws1 >>. identifier)
(ws1 >>. literal) // If I put 'pexpr', it doesn't work too...
(ws1 >>. literal)
(statements)
(fun id min max stmts -> Loop(id, min, max, stmts))
let print = keyword "print" >>. (ws1 >>. identifier |>> Print)
let statement =
attempt plet <|>
attempt print <|>
attempt ploop <|>
attempt pexpression
statementsRef := indentedMany1 statement "statement"
let document = statements .>> spaces .>> eof
let test str =
match runParserOnString document (UserState.Create()) "" str with
| Success(result, _, _) -> printfn "Success: %A" result
| Failure(errorMsg, _, _) -> printfn "Failure: %s" errorMsg
System.Console.Clear()
test @"
loop i 0 10
let myVar = 2 + 1
print myVar
"
我知道我同时问了好几个问题，而且网站确实不允许，但它们都有点联系在一起，所以我还不如一石二鸟...
我真的很想了解我的错误，以便为非常小的 ML-like 语言设计一个解析器。
谢谢。
编辑
这是我当前的代码，已修改以响应遇到的第一个缩进问题：
open IndentationParserWithoutBacktracking // So from the link
let isBlank = fun c -> c = ' ' || c = '\t'
let ws = spaces
let ws1 = skipMany1SatisfyL isBlank "whitespace"
let str s = pstring s .>> ws
let keyword str = pstring str >>? nextCharSatisfiesNot (fun c -> isLetter c || isDigit c) <?> str
// AST
type Identifier = Identifier of string
type Value =
| Int of int
| Float of float
| Bool of bool
| String of string
| Char of char
| Variable of Identifier
// In FP, "all" is an expression, so:
type Expr =
// Arithmetic + lists and tuple
| Literal of Value
| Infix of Expr * InfixOp * Expr
| List of Expr list
| Tuple of Expr list
// Statements
| Return of Expr
| Loop of Identifier * Expr * Expr * Expr list
| Print of Identifier
and InfixOp =
| Sum | Sub | Mul | Div | Pow | Mod
| And | Or | Equal | NotEqual | Greater | Smaller | GreaterEqual | SmallerEqual
// Literals
let numberFormat = NumberLiteralOptions.AllowMinusSign ||| NumberLiteralOptions.AllowFraction |||
NumberLiteralOptions.AllowHexadecimal ||| NumberLiteralOptions.AllowOctal |||
NumberLiteralOptions.AllowBinary
let literal_numeric =
numberLiteral numberFormat "number" |>> fun nl ->
if nl.IsInteger then Literal (Int(int nl.String))
else Literal (Float(float nl.String))
let literal_bool =
(choice [
(stringReturn "true" (Literal (Bool true)))
(stringReturn "false" (Literal (Bool false)))
]
.>> ws) <?> "boolean"
let literal_string =
(between (pstring "\"") (pstring "\"") (manyChars (satisfy (fun c -> c <> '"')))
|>> fun s -> Literal (String s)) <?> "string"
let literal_char =
(between (pstring "'") (pstring "'") (satisfy (fun c -> c <> '''))
|>> fun c -> Literal (Char c)) <?> "character"
let identifier =
(many1Satisfy2L isLetter (fun c -> isLetter c || isDigit c) "identifier"
|>> fun i -> Identifier i) <?> "identifier"
let betweenParentheses p =
(between (str "(") (str ")") p) <?> ""
let variable = identifier |>> fun id -> Literal (Variable id)
let literal = (attempt literal_numeric <|>
attempt literal_bool <|>
attempt literal_char <|>
attempt literal_string <|>
attempt variable) <?> "literal"
// Expressions and statements
let pexprs, pexprimpl = createParserForwardedToRef()
// `ploop` is located here to force `pexprs` to be of the type `Expr list`, `ploop` requesting an expression list.
let ploop =
pipe4
(keyword "loop" >>. ws1 >>. identifier)
(ws1 >>. literal)
(ws1 >>. literal)
(pexprs)
(fun id min max stmts -> Loop(id, min, max, stmts))
// `singlepexpr` allows to use only one expression.
let singlepexpr =
pexprs |>> fun ex -> ex.Head
let term =
(ws >>. singlepexpr .>> ws) <|>
(betweenParentheses (ws >>. singlepexpr)) <|>
(ws >>. literal .>> ws) <|>
(betweenParentheses (ws >>. literal))
let infixOperator (p: OperatorPrecedenceParser<_, _, _>) op prec map =
p.AddOperator(InfixOperator(op, ws, prec, Associativity.Left, map))
let ops =
// Arithmetic
[ "+"; "-"; "*"; "/"; "%" ] @
// Logical
[ "&&"; "||"; "=="; "!="; ">"; "<"; ">="; "<=" ]
let opCorrespondance op =
match op with
// Arithmetic operators
| "+" -> Sum
| "-" -> Sub
| "*" -> Mul
| "/" -> Div
| "%" -> Mod
// Logical operators
| "&&" -> And
| "||" -> Or
| "==" -> Equal
| "!=" -> NotEqual
| ">" -> Greater
| "<" -> Smaller
| ">=" -> GreaterEqual
| "<=" -> SmallerEqual
let opParser = new OperatorPrecedenceParser<Expr, unit, UserState>()
for op in ops do
infixOperator opParser op 1 (fun x y -> Infix(x, opCorrespondance op, y))
opParser.TermParser <- term
let list = (between (str "[") (str "]") (sepBy singlepexpr (str ",")) |>> List) <?> "list"
let tuple = (between (str "(") (str ")") (sepBy singlepexpr (str ",")) |>> Tuple) <?> "tuple"
// Statements
// A commented `let` expression, commented for tests with the `return` instruction.
//let plet =
// pipe3
// (keyword "let" >>. ws1 >>. identifier)
// (ws >>. gtt ":")
// (ws >>. str "=" >>. ws >>. pexprs)
// (fun id gtt exp -> Let(id, gtt, exp))
let preturn =
keyword "return" >>. ws >>. singlepexpr
|>> fun ex -> Return ex
let print = keyword "print" >>. (ws1 >>. identifier |>> Print)
let instruction =
print <|>
ploop <|>
preturn <|>
opParser.ExpressionParser <|> // So we add the arithmetic, like x + y or 21 * 32 - 12 for example
list <|>
tuple <|>
literal
pexprimpl := indentedMany1 instruction "instruction"
let document = pexprs .>> spaces .>> eof
let test str =
match runParserOnString document (UserState.Create()) "" str with
| Success(result, _, _) -> printfn "%A" result
| Failure(errorMsg, _, _) -> printfn "%s" errorMsg
System.Console.Clear()
// The test code that give an error of "newline" expecting
let code = test @"
return 2 + 1
"
这里有一些关于错误的截图：
为什么 indentedMany1 告诉你它在你的示例代码中期待一个换行符是因为它正在寻找：一个缩进的 块 。不是一行中的一个表达式。所以你的 let myVar = 2 + 1 行混淆了它。如果你写成：
let myVar =
2 + 1
那我打赌它会起作用。
我相信，您需要的是更改 let 解析器以允许以下两种情况之一：或者 单行表达式， 或 语句块（您的 statements 解析器）。即，类似于：
let pLetValue = expression <|> statements
let plet =
pipe2
(keyword "let" >>. ws1 >>. identifier)
(ws >>. str "=" >>. ws >>. pLetValue)
(fun id gtt exp -> Let(id, gtt, exp))
请注意，我还没有对此进行测试，因为我今天没有太多时间。您可能需要 attempt expression（或 pexpr，两者是一回事），而不是上面的 expression。稍微试验一下，看看会发生什么；如果您在尝试弄清楚 FParsec 如何处理给定表达式时完全迷失了方向，请记住 http://www.quanttec.com/fparsec/users-guide/debugging-a-parser.html.