parse-measurement

Description

Parse a string containing a measurement, e.g., "3pi" or "2.5in", and return the magnitude and units: (3 "pi") or (2.5 "in").

Either element of the list may be #f if the string cannot reasonably be parsed as a measurement. Leading and trailing spaces are ignored.

Author

Norman Walsh, <ndw@nwalsh.com>

Source Code

(define (parse-measurement measure)
  ;; Parse a string containing a measurement and return the magnitude and units
  (let* ((magstart  (find-first-char measure " " "0123456789."))
	 (unitstart (find-first-char measure " 0123456789." ""))
	 (unitend   (find-first-char measure "" " " unitstart))
	 (magnitude (if (< magstart 0)
			#f
			(if (< unitstart 0)
			    (substring measure 
				       magstart 
				       (string-length measure))
			    (substring measure magstart unitstart))))
	 (unit      (if (< unitstart 0)
			#f
			(if (< unitend 0)
			    (substring measure 
				       unitstart 
				       (string-length measure))
			    (substring measure unitstart unitend)))))
  (list magnitude unit)))