The New ‘Absent Operator’ in Ruby’s Regular Expressions

Re:The New ‘Absent Operator’ in Ruby’s Regular Expressions by ebiester on Thursday March 23, 2017 @03:36PM (#13943390)

Icon (and SNOBOL before that) had an alternate syntax that was more verbose but more readable.

  s := "this is a string"
    s ? {                               # Establish string scanning environment
        while not pos(0) do  {          # Test for end of string
            tab(many(' '))              # Skip past any blanks
            word := tab(upto(' ') | 0)  # the next word is up to the next blank -or- the end of the line
            write(word)                 # write the word
        }
    }

I should implement something like this in ruby some day... (I did it in java long ago, but this was before you just threw things up to github and I have long since lost it.)

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Re:The New ‘Absent Operator’ in Ruby’s Regular Expressions by sublimeloge on Thursday March 23, 2017 @07:06PM (#13945159)

For those who haven't seen the language before, I think it's also useful to know what expression evaluation in Icon works using a recursive backtracking algorithm. This means that the most natural way of writing a string scanning parser (like the one above) more or less automatically gives you a recursive backtracking parser. Like ebiester, I too have found it to be a nice way to do certain kinds of simple string parsing.

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Re:The New ‘Absent Operator’ in Ruby’s Regular Expressions by norswap on Thursday March 23, 2017 @07:28PM (#13945302)

Nice notation. Looks like a grammar with a bit more fancyness thrown in. I have a tool that does this kind of stuff: https://github.com/norswap/whimsy/blob/master/doc/autumn/REA...

I should try to implement something like this, to see how hard it would be (I think not too much, but I might overlook something).

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