Subject: Re: bug#21944: Error on ordering of define-record-type and define-public in a module is unhelpful - possible improvement?

From: Andy Wingo <[email-masked]>
Date: Mon, 27 Jun 2016 10:02:37 +0200

On Sun 26 Jun 2016 23:06, Andy Wingo <[email-masked]> writes:

> On Tue 17 Nov 2015 09:27, Koz Ross <[email-masked]> writes:
>
>> I have the following file, called foo.scm:
>>
>> (define-module (koz foo)
>>  #:use-module (srfi srfi-9))
>>
>> (define-public (make-empty-bar)
>>   (make-bar #f))
>>
>> (define-record-type <bar>
>>   (make-bar open)
>>   bar?
>>   (open bar-open set-bar-open!))
>
>> Would it be possible for the error message in this case to be a bit
>> more helpful? Even better, would it be possible to not make this an
>> issue when compiling?
>
> It would be possible to make the scope of make-bar be the whole file.
> In theory it should work I guess, given this news entry from 2.0.1:
>
>   ** `begin' expands macros in its body before other expressions

Apparently the reason this doesn't work in Guile right now is that the
compiler currently reads and compiles one Scheme expression at a time,
then stitches them together on the Tree-IL level.  Incidentally,
`primitive-load' works in the same way for the interpreter: it reads and
eval's single expressions in a loop.  We could change this to have Guile
read the whole file and pass it all to the expander at once, within a
`begin'.  This has some user-visible changes though:

  * if evaluating an expression throws an error, primitive-load doesn't
    read the following expressions and so doesn't detect syntax errors;
    try a file like this:

    (error "what")
    )

    With the interpreter (primitive-load) you will get the "what" error,
    not a syntax error.  (Yes the unclosed paren hurts my eyeballs but I
    wanted to demonstrate a syntax error.  Here's a matching paren:
    ")".)

  * Procedural macros won't be able to use bindings defined previously
    in the file unless they are eval-whenned.  Of course this already
    breaks in the compiler, but it succeeds in the interpreter.

Maybe now is a good time to do this though, in 2.2.  Ludovic, Mark:
thoughts?

Andy