Ricardo Wurmus <rek...@elephly.net> writes:
> Hi,
>
>> Consider this bit of simple code:
>>
>> #+BEGIN_SRC scheme
>>
>> (define (thunk)
>> (lambda (x)
>> x))
>>
>> (thunk) ;; works ok, I guess.
>> (thunk "hello world!\n") ;; runtime error
>>
>> ;;; <stdin>:1074:0: warning: possibly wrong number of arguments to `thunk'
>> ice-9/boot-9.scm:1669:16: In procedure raise-exception:
>> Wrong number of arguments to #<procedure thunk ()>
>>
>> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
>> #+END_SRC
>>
>> Guile will compile this program seemingly with no error. Guile will
>> correctly report at runtime that procedure '(thunk "hello world!\n")'
>> takes no arguments, but it's lambda accepts 1 argument. Would it be
>> possible to report this error at compile time? Would that be
>> advantageous?
>
> This is not a bug. What you call “thunk” here is a procedure that
> returns a procedure. That’s very common and is often done to delay
> evaluation.
>
> It is in fact an error to call the procedure “thunk” with an argument.
> It doesn’t matter that it happens to return a procedure that *can* take
> an argument. The procedure it returns is just like any other value,
> though, and isn’t inspected any further.
>
> That said, it is not true that Guile will compile this without a
> complaint. I dumped your code snippet in a file foo.scm and
> compiled it:
>
> guild compile foo.scm
> foo.scm:6:0: warning: wrong number of arguments to `thunk'
> wrote
> `/home/rekado/.cache/guile/ccache/3.0-LE-8-4.4/home/rekado/dev/gx/gwl/foo.scm.go'
>
> Isn’t that exactly what you’re asking for?
Gotcha. Thanks for explaining! I suppose what I meant to say is,
should guile refuse to compile the above? In other languages, like C I
suppose, writing a function simultaneous with one and two arguments
would refuse to compile. The compiler would make you fix the code.
Should guile do this as well?
When I look at
#+BEGIN_SRC scheme
(define (thunk)
(lambda (x)
x))
#+END_SRC
or
#+BEGIN_SRC scheme
(use-modules
(srfi srfi-9))
(define-record-type <lunch>
(make-lunch food duration location)
lunch?
(food lunch-food)
(duration lunch-duration)
(location lunch-location))
(define dine-out
(make-lunch "pizza" "30 min" "downtown"))
;; maybe this should refuse to compile?
(define (list-lunch)
(match-lambda (($ <lunch> food duration location )
(list food duration location))))
#+END_SRC
My thought is, this is clearly a mistake. This person needs to change
the above code.
Thanks,
Joshua
P.S. I'm not a scheme expert. I'm only reporting this, because I
recently read a blog post about free software users rarely report
perceived issues. I'm just trying to be helpful. :) Thanks for the
speedy response time.
--
Joshua Branson (joshuaBPMan in #guix)
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