Re: REPL and load deifferences (was Re: Proposal for a new (ice-9 history))

[Mikael Djurfeldt <mikael@djurfeldt.com>]

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And, the attachments...

On Tue, Oct 30, 2018 at 11:21 AM Mikael Djurfeldt <mikael@djurfeldt.com>
wrote:

> On Tue, Oct 30, 2018 at 1:55 AM Mikael Djurfeldt <mikael@djurfeldt.com>
> wrote:
>
>> On Tue, Oct 30, 2018 at 12:55 AM Mark H Weaver <mhw@netris.org> wrote:
>>
>>>   More precisely, it is a literal
>>> identifier recognized by 'match' and related macros, in the same sense
>>> that 'else' and '=>' are literal identifiers recognized by the 'cond'
>>> macro.
>>>
>>> R5RS section 4.3.2 (Pattern language) specifies how these literal
>>> identifiers are to be compared with identifiers found in each macro use:
>>>
>>>      Identifiers that appear in <literals> are interpreted as literal
>>>      identifiers to be matched against corresponding subforms of the
>>>      input.  A subform in the input matches a literal identifier if and
>>>      only if it is an identifier and either both its occurrence in the
>>>      macro expression and its occurrence in the macro definition have
>>>      the same lexical binding, or the two identifiers are equal and both
>>>      have no lexical binding.
>>>
>>> The implication is that these literal identifiers such as 'else', '=>'
>>> and '$' lose their special meaning in any environment where they are
>>> bound, unless the same binding is visible in the corresponding macro
>>> definition environment.  R6RS and R7RS also specify this behavior.
>>>
>>> For example:
>>>
>>> --8<---------------cut here---------------start------------->8---
>>> mhw@jojen ~$ guile
>>> GNU Guile 2.2.3
>>> Copyright (C) 1995-2017 Free Software Foundation, Inc.
>>>
>>> Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
>>> This program is free software, and you are welcome to redistribute it
>>> under certain conditions; type `,show c' for details.
>>>
>>> Enter `,help' for help.
>>> scheme@(guile-user)> ,use (ice-9 match)
>>> scheme@(guile-user)> ,use (srfi srfi-9)
>>> scheme@(guile-user)> (define-record-type <foo> (make-foo a b) foo? (a
>>> foo-a) (b foo-b))
>>> scheme@(guile-user)> (match (make-foo 1 2) (($ <foo> a b) (+ a b)))
>>> $1 = 3
>>> scheme@(guile-user)> (define $ 'blah)
>>> scheme@(guile-user)> (match (make-foo 1 2) (($ <foo> a b) (+ a b)))
>>> <unnamed port>:6:0: Throw to key `match-error' with args `("match" "no
>>> matching pattern" #<<foo> a: 1 b: 2>)'.
>>>
>>> Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
>>> scheme@(guile-user) [1]>
>>> --8<---------------cut here---------------end--------------->8---
>>>
>>
>> Incidentally, this does *not* throw an error in master (unless I made
>> some mistake in this late hour), which then is a bug!
>>
>
> I now looked at this a bit more. It turns out that the difference is not
> between stable-2.2 and master, but between REPL and load. While I can
> reproduce the above also in master, if I instead load it (attached file
> matchcoll.scm), I get no error!
>
> Also, the following file (attached as "elsetest.scm"):
> ------------------------------
> (display (cond (else #t)))
> (newline)
>
> (define else #f)
>
> (display (cond (else #t)))
> (newline)
> ------------------------------
>
> gives the results #t and #<unspecified>, as expected, in the REPL, but if
> I load the file, I instead get:
>
> scheme@(guile-user)> (load "elsetest.scm")
> /home/mdj/guile/elsetest.scm:7:0: Unbound variable: else
>
> If I load it into Chez Scheme, I get:
>
> #t
> #<void>
>
> as expected.
>
> Maybe someone more knowledgeable than myself could sort out what out of
> this is a bug?
>
> Also, I have to rant a bit about R5RS section 4.3.2. What a mess this is!
> To have the literals influenced by bindings outside goes against the spirit
> of lexical binding, in my opinion, where the idea is to be able to judge
> the outcome of the code from looking at it locally.
>
> Best regards,
> Mikael
>
>

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(use-modules (ice-9 match))
(use-modules (srfi srfi-9))
(define-record-type <foo> (make-foo a b) foo? (a foo-a) (b foo-b))
(match (make-foo 1 2) (($ <foo> a b) (+ a b)))

(define $ 'blah)
(match (make-foo 1 2) (($ <foo> a b) (+ a b)))

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(display (cond (else #t)))
(newline)

(define else #f)

(display (cond (else #t)))
(newline)