I am writing a parser in which I want to parse arithmetic expressions like: /hdfs://xxx.xx.xx.x:xxxx/path1/file1.jpg+1 I want to parse it change the infix to postfix and do the calculation. I used helps from a part of code in another discussion as well.
class InfixToPostfix extends StandardTokenParsers {
import lexical._
def regexStringLit(r: Regex): Parser[String] = acceptMatch(
"string literal matching regex " + r,
{ case StringLit(s) if r.unapplySeq(s).isDefined => s })
def pathIdent: Parser[String] =regexStringLit("/hdfs://([\d\.]+):(\d+)/([\w/]+/(\w+\.\w+))".r)
lexical.delimiters ++= List("+","-","*","/", "^","(",")",",")
def value :Parser[Expr] = numericLit ^^ { s => Number(s) }
def variable:Parser[Expr] = pathIdent ^^ { s => Variable(s) }
def parens:Parser[Expr] = "(" ~> expr <~ ")"
def argument:Parser[Expr] = expr <~ (","?)
def func:Parser[Expr] = ( pathIdent ~ "(" ~ (argument+) ~ ")" ^^ { case f ~ _ ~ e ~ _ => Function(f, e) })
def term = (value | parens | func | variable)
// Needed to define recursive because ^ is right-associative
def pow :Parser[Expr] = ( term ~ "^" ~ pow ^^ {case left ~ _ ~ right => BinaryOperator(left, "^", right) }|
term)
def factor = pow * ("*" ^^^ { (left:Expr, right:Expr) => BinaryOperator(left, "*", right) } |
"/" ^^^ { (left:Expr, right:Expr) => BinaryOperator(left, "/", right) } )
def sum = factor * ("+" ^^^ { (left:Expr, right:Expr) => BinaryOperator(left, "+", right) } |
"-" ^^^ { (left:Expr, right:Expr) => BinaryOperator(left, "-", right) } )
def expr = ( sum | term )
def parse(s:String) = {
val tokens = new lexical.Scanner(s)
phrase(expr)(tokens)
}
//and the rest of the code
I was able to solve the following errors with the help of this answer:
ScalaParser.scala:192: invalid escape character
[error] def pathIdent: Parser[String] =regexStringLit("/hdfs://([\d\.]+):(\d+)/([\w/]+/(\w+\.\w+))".r)
[error] ^
[error] ScalaParser.scala:192: invalid escape character
[error] def pathIdent: Parser[String] =regexStringLit("/hdfs://([\d\.]+):(\d+)/([\w/]+/(\w+\.\w+))".r)
[error] ^
[error] ScalaParser.scala:192: invalid escape character
[error] def pathIdent: Parser[String] =regexStringLit("/hdfs://([\d\.]+):(\d+)/([\w/]+/(\w+\.\w+))".r)
[error] ^
With the change of pathIdent to this:
def pathIdent: Parser[String] =regexStringLit("/hdfs://([\\d.]+):(\\d+)/([\\w/]+/(\\w+\\.w+))".r)
Now I am getting a run time error which says:
[1.1] failure: string literal matching regex /hdfs://([\d\.]+):(\d+)/([\w/]+/(\w+\.\w+)) expected
/hdfs://111.33.55.2:8888/folder1/p.a3d+1
^
It was working using JavaTokenParsers but with current changes and I had to use StandardTokenParsers.
In a double quoted string backslash is an escape character. If you mean to use the literal backslash in a double quotes string you must escape it, thus
"\d"
should be"\\d"
.Furthermore you do not need to escape the regex dot within a character class, since dot has no special meaning with a character class. So
"[\d.]"
should just be "[\d.]".You can also forgo all this escaping business by using the raw interpolator or multi-line string literals using triple quotes.