parser-combinators

问题 Im trying to match this syntax: pgm ::= exprs exprs ::= expr [; exprs] expr ::= ID | expr . [0-9]+ My scala packrat parser combinator looks like this: import scala.util.parsing.combinator.PackratParsers import scala.util.parsing.combinator.syntactical._ object Dotter extends StandardTokenParsers with PackratParsers { lexical.delimiters ++= List(".",";") def pgm = repsep(expr,";") def expr :Parser[Any]= ident | expr~"."~num def num = numericLit def parse(input: String) = phrase(pgm)(new

问题 I have a list of values from which I can construct a list of parsers, that depend on these values by mapping (see example). Then what I want to do is turn the list of parsers into a single parser by concatenation. One possibility is using foldLeft and ~ : parsers.foldLeft(success(Nil)){case (ps,p) => rs ~ p ^^ {case xs ~ x => x ::xs}} ^^ (_.reverse) Is this efficient? I don't know how combinator parsers work; will there be a call stack with depth of length of the list? Thus may I run into SO

问题 I have created a Scala parser combinator to filter data records based on the answer I got to an previous question How to parse a string with filter citeria in scala and use it to filter objects I would like to add the calculator parser combinator from the answer to this question Operator Precedence with Scala Parser Combinators to the bottom of the parser combinator that I created based on the first question. The calculator parser combinator therefore needs to accept a dataRecord so that an

问题 What is the problem with parsing the blank/whitespace? scala> object BlankParser extends RegexParsers { def blank: Parser[Any] = " " def foo: Parser[Any] = "foo" } defined module BlankParser scala> BlankParser.parseAll(BlankParser.foo, "foo") res15: BlankParser.ParseResult[Any] = [1.4] parsed: foo scala> BlankParser.parseAll(BlankParser.blank, " ") res16: BlankParser.ParseResult[Any] = [1.2] failure: ` ' expected but ` ' found ^ scala> 回答1: the lexer for scala throws blankspaces away. try

问题 Lets see the code snippet: pSegmentBegin p i = pIndentExact i *> ((:) <$> p i <*> ((pEOL *> pSegment p i) <|> pure [])) if I change this code in my parser to: pSegmentBegin p i = do pIndentExact i ((:) <$> p i <*> ((pEOL *> pSegment p i) <|> pure [])) I've got an error: canot compute minmal length of a parser due to occurrence of a moadic bind, use addLength to override I thought the above parser should behave the same way. Why this error can occur? EDIT The above example is very simple (to

问题 Is there a convenient way to use Scala's parser combinators to parse languages where indentation is significant? (e.g. Python) 回答1: Let's assume we have a very simple language where this is a valid program block inside the block and we want to parse this into a List[String] with each line inside the block as one String . We first define a method that takes a minimum indentation level and returns a parser for a line with that indentation level. def line(minIndent:Int):Parser[String] = repN

问题 The task is find particular key-value pairs and parse them. The pairs can occur in any order. My partially working attempt: open FParsec type Parser<'a> = Parser<'a, unit> type Status = Running | Done type Job = { Id: int Status: Status Count: int } let ws = spaces let jobId: Parser<int> = ws >>. skipStringCI "Job id" >>. ws >>. skipChar '=' >>. ws >>. pint32 let status: Parser<Status> = ws >>. skipStringCI "Status" >>. ws >>. skipChar '=' >>. ws >>. ( (skipStringCI "Running" >>% Running) <|>

问题 Can someone explain how and when to use the triple caret ^^^ (vs the double caret ^^) when designing scala parser combinators? And also when / how to use the parser.into() method (>>). 回答1: I'll begin with an example using Scala's Option type, which is similar in some important ways to Parser , but can be easier to reason about. Suppose we have the following two values: val fullBox: Option[String] = Some("13") val emptyBox: Option[String] = None Option is monadic, which means (in part) that

问题 I've tried /* inside RegexParser class */ def exp : Parser[Exp] = term~addop_chain ^^ {case l~ThenAdd(optype,r) => AritOp(l,optype,r)} def addop_chain : Parser[Exp] = ("+"|"-")~term~addop_chain ^^ {case sym~term~ThenAdd(optype,r) => ThenAdd(sym, AritOp(term,optype,r)) } | ("+"|"-")~term ^^ {case sym~term => ThenAdd(sym, term)} def term = /* right now, only int literal. code unrelevant */ /* Case classes for storing: */ case class ThenAdd(sym: String, r: Exp) case class AritOp(l: Exp, sym:

问题 import scala.util.parsing.combinator._ object ExprParser extends JavaTokenParsers { lazy val name: Parser[_] = "a" ~ rep("a" | "1") | function_call lazy val function_call = name ~ "(" ~> name <~ ")" } recurs indefinitely for function_call.parseAll("aaa(1)") . Obviously, it is because 1 cannot inter the name and name enters the function_call , which tries the name, which enters the funciton call. How do you resolve such situations? There was a solution to reduce name to simple identifier def