global defs    # shared definitions
  const MAXPATTERN := 20
  const MAXFILENAME := 20
  const MAXLINE := 120
end

resource grep()
  import defs
  var pattern: string[MAXPATTERN]; getarg(1, pattern)
  var filename: string[MAXFILENAME]; getarg(2, filename)
  var fd: file := open(filename, READ)

  var line[2]: string[MAXLINE]
  var ln := 1

  procedure find(pattern, line: string[*])
    # if line contains pattern, write out line
    var i := 1, plen := length(pattern)
    do i <= (length(line) - plen + 1) ->
      if pattern = line[i:i+plen-1] ->
          write(filename || ":", line); return
      fi
      i++
    od
  end

  procedure doread(ln: int) returns result: int
    result := read(fd, line[ln])
  end

  var start := age()
  # find all instances of pattern in filename
  var result := doread(ln)
  do result != EOF ->
    co find(pattern, line[ln])
    // result := doread(3-ln)
    oc
    ln := 3-ln
  od
  var finish := age()
  write("execution time is", finish-start)

end