Gaucheマニュアルのgrepサンプルを改造してみる。

grep.scm

#!/usr/bin/env gosh

(use util.match)
; マニュアルからコピー

(define (usage)
  (format (current-error-port)
          "Usage: ~a regexp file ...\n" *program-name*)
  (exit 2))

(define (grep rx port)
  (with-input-from-port port
    (lambda ()
      (port-for-each
       (lambda (line)
         (when (rxmatch rx line)
           (format #t "~a:~a: ~a\n"
                   (port-name port)
                   (- (port-current-line port) 1)
                   line)))
       read-line))))

(define (call-with-<> files proc :optional (reader #f))
  (cond
    [ (input-port? files)
     (if reader
       (port-for-each proc (cut reader files) ) 
       (proc files) )  ]
    [ (string? files) 
     (call-with-input-file files (cut call-with-<> <> proc reader) ) ]
    [ (list? files)
     (for-each (cut call-with-<> <> proc reader) files) ] 
    [else (error "error")]
    ))

(define (main args)
  (if (null? (cdr args))
    (usage)
    (let ((rx (string->regexp (cadr args))))
      (call-with-<> 
        (match (cddr args)
          [() (current-input-port)] [x x] )
        (cut grep rx <>))))
  0)