Calculate mathematical operation stored in String using regex in Scala

Question

I want to evaluate mathematical expression stored in String and print the result.

I have to use Pattern matching in Scala. I wrote this code below, but it does not work, it prints false instead of 2.

Any help will be appreciated.

object PatternMatcher{
    val s = "13 - 5 - 6"
    val Pattern = "((\\d+\\s[+-]\\s){1,10}(\\d+){0,1})".r

    def main(args: Array[String]) {
        println(matcher(s))
    }

    def matcher(choice: String): Any = choice match {
        case Pattern(choice) => choice
        case _ => "false"
    }
}

A capturing group inside a capturing group...? Is that what you wanted to do ? — Thomas Ayoub
– Thomas Ayoub, Commented Jan 27, 2016 at 13:21
@Thomas I think yes, because I want to capture whole string. When i used one group( \\d+\\s[+-]\\s){1,10}\\d+) i got only 5 - as a result, which is the last part of the string matched with the pattern. — user3463645
– user3463645, Commented Jan 27, 2016 at 13:29
If you try with this: (\d+\s+[-+]\s+\d+\s+[-+]\s+\d) (to be escaped) does it work? — Thomas Ayoub
– Thomas Ayoub, Commented Jan 27, 2016 at 13:31
@Thomas Oh, I didn't mention that i want to expand this equation, by adding or subtract more numbers. So your solution works but only for this example, with 3 numbers. — user3463645
– user3463645, Commented Jan 27, 2016 at 13:48

Thomas Ayoub · Accepted Answer · 2016-01-27 15:12:55Z

1

If you want something flexible, this is what you need:

((?:\d+\s*[-+]\s+)*\d+)

With Live Demo

edited Jan 27, 2016 at 15:12

answered Jan 27, 2016 at 13:53

Thomas Ayoub

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5 Comments

user3463645 Over a year ago

I'm getting exception: Unknown inline modifier near index 3 ((?|\d+\s*[-+]\s+)*\d+) It points on | (logical OR)

Thomas Ayoub Over a year ago

@user3463645 the regex I gave you is unescaped, you should escape it before using it (using \ )

user3463645 Over a year ago

I can't get it to work, could you write exactly how the Pattern variable should look like.

Thomas Ayoub Over a year ago

@user3463645 my bad. It's a : instead of |

user3463645 Over a year ago

Great, now it's working. I have used """((?:\d+\s*[-+]\s+)*\d+)""" so there is no need to escape string.

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