Re: Adding wc to Bournish

[Taylan Ulrich Bayırlı/Kammer]

Eric Bavier <address@hidden> writes:

> On 2016-05-26 14:27, Efraim Flashner wrote:
>> Here's where I'm currently at with 'wc'. Currently I'm getting an error
>> about having the wrong number of arguments for lambda (I assume)
> [...]
>> +(define (wc-command file)
>> +  ((lambda (lines words chars) ; lambda doesn't like 3 variables
>> +     (format #t "~a ~a ~a ~a~%" lines words chars file))
>> +   (call-with-input-file file lines+chars)))
> [...]
>>
>> ;;; /home/efraim/workspace/guix/guix/build/bournish.scm:143:2: warning:
>> wrong number of arguments to `#<tree-il (lambda () (lambda-case
>> (((lines
>> words chars) #f #f #f () (lines-24244 words-24245 chars-24246)) (apply
>> (toplevel format) (const #t) (const "~a ~a ~a ~a~%") (lexical lines
>> lines-24244) (lexical words words-24245) (lexical chars chars-24246)
>> (lexical file file-24242)))))>'
>
> I think you might just be missing a 'call-with-values':
>
> (define (wc-command file)
>   (call-with-values
>     (call-with-input-file file lines+chars)
>     (lambda (lines words chars) ...)))

I believe this should be

    (define (wc-command file)
      (call-with-values
        (lambda ()
          (call-with-input-file file lines+chars))
        (lambda (lines words chars)
          ...)))

since both arguments to call-with-values must be procedures.


By the way, I prefer SRFI-11 let-values (standardized in R7RS):

    (define (wc-command file)
      (let-values (((lines words chars)
                    (call-with-input-file file lines+chars)))
        ...))

The large number of parentheses involved are annoying at first, but as I
used it more often I grew accustomed to it and aren't bothered at all
anymore, neither in writing nor reading the code.  I also had some valid
uses of let*-values occasionally; I find it neat how it allows "piping"
a number of different values through a sequence of procedures, without
having to allocate any intermediate data structures.

Taylan