On 25-02-2023 01:15, Matt Wette wrote:
> On 2/24/23 3:51 PM, Maxime Devos wrote:
>> On 25-02-2023 00:48, Maxime Devos wrote:
>>>>> (**) For compatibility with Racket, it's not like we couldn't
>>>>> implement both "#lang" and "-*- stuff: language -*-".
>>
>> TBC, I mean ‘only support #lang' for values of 'lang' that Racket 
>> supports’, or alternatively ‘support #lang for compatibility, but 
>> recommend -*- ... -*- in the Guile manual.’.
> 
> The point of this is to tell the compiler what language it needs to parse,
> if not the default (Scheme).  Using `#lang pascal' or `#!lang pascal' 
> allows
> the compiler to figure this out in the first few characters read. Using
> `-*- lang: pascal -*-' might require the compiler to read a lot of text 
> (not knowing
> if what text is comment or not) to determine if language has been 
> specified.
> For the `-*-' based design, is there a maximum number of characters to be
> read before deciding?

Guile already searches for '-*- ... -*-' lines, as mentioned in a 
previous message:

> (*) The port encoding detection supports "-*- coding: whatever -*-",
> presumably that functionality could be reused. 

As such, it shouldn't incur an overly large cost to support '-*- 
something: modula -*-' too.

On the character limit: according to Emacs documentation, there is a 
line limit: the '-*- ... -*-' must be on the first line.  (See: 
‘(emacs)Specifying File Variables’.) This seems the same situation like 
'#lang' to me; not ‘a lot of text’.

A more explicit character limit of 'first few hundred bytes' is 
mentioned in see the documentation of 'file-encoding':

  -- Scheme Procedure: file-encoding port
  -- C Function: scm_file_encoding (port)
      Attempt to scan the **first few hundred bytes** from the PORT for
      hints about its character encoding.  Return a string containing the
      encoding name or ‘#f’ if the encoding cannot be determined.  The
      port is rewound.

      Currently, the only supported method is to look for an Emacs-like
      character coding declaration (*note how Emacs recognizes file
      encoding: (emacs)Recognize Coding.).  The coding declaration is of
      the form ‘coding: XXXXX’ and must appear in a Scheme comment.
      Additional heuristics may be added in the future.

Greetings,
Maxime.