Re: Regexp Functions

[Aaron Hill]

On 2020-06-15 11:16 pm, Freeman Gilmore wrote:
> "y" could represent  one of my accidentals, "-y" inverted.   "-ax3" ,
> one of my accidentals ,
> "-a" used 3 times; like a flag, but needs to be inverted to "-x3".
> "+rx2" needs a space like "+r x2".   "t" standard accidental. All "+" 
> removed.
> "-y -ax3 +rx2 -stx2 t" becomes "-y -a -x3 r x2 -st -x2 t" , then 
> convert to list
>  ("-y" "-a" "-x3" "r" "x2" "-st" "-x2" "t").

This is sounding much more like you have invented a language/grammar 
that needs to be parsed rather than simply wanting to apply some 
arbitrary text transformation.  The interest in string manipulation 
stems from wanting to support a form of shorthand within the microtonal 
ligature notation.

To that end, allow me to present an alternate way to attack the problem. 
 Consider:

;;;;
(apply append
  (map (lambda (m)
         (let ((inv (or (match:substring m 2) "")))
           (map (lambda (s) (string-append inv s))
                (filter
                  (lambda (s) (not (string-null? s)))
                  (map (lambda (n) (or (match:substring m n) ""))
                       '(3 4))))))
       (list-matches
         "((-)|\\+?)([a-z]*)(x[0-9]+)?"
         "-y -ax3 +rx2 -stx2 t")))
;;;;
====
("-y" "-a" "-x3" "r" "x2" "-st" "-x2" "t")
====

Several assumptions are being made within the core regular expression 
above; but what is important to note is that we are not doing any text 
substitution of the original input.  Rather, we are using a regular 
expression to identify the valid "words" and extract the key parts of 
those words.  While you can certainly act upon the information right 
away, I am showing a way to build a list of strings that should meet 
your specification.


-- Aaron Hill