[racket] Looking for awk examples

The awk macro refers to the documentation in scsh; there are examples
of the awk macro there in:

    http://www.scsh.net/docu/html/man-Z-H-9.html#node_sec_8.2.1


Some of the examples there may need some adaptation, as I don't think
Racket has an "sre" library to support the writing regexps with
s-expressions.  Here's one adapted example:

Example:

#lang racket/base
(require mzlib/awk)

;; Reads the number of uncommented lines
(awk (read-line) (line) ((nlines 0))
  ("^\\s*;"  nlines)              ; A comment line.
  (else (+ nlines 1)))            ; Not a comment line.


The original sre for this was (: bos (* white) ";"), which I've
translated to a string representation that appears to be effective.
But it's not obvious from the documentation what kind of regular
expression strings are allowed by this mzlib/awk library, though.



Related: it's one of the "Larger Projects" proposed on the wiki, to
make a modern #lang scsh:

    https://github.com/plt/racket/wiki/Intro-Projects