[plt-scheme] an r6rs library compatible repl?

From: Rohan Drape (rohan.drape at gmail.com)
Date: Wed Mar 19 06:04:20 EDT 2008

a reworked question first, reply below.

the actual problem i have is related to 
mpairs.  i've an r6rs library that i'd 
like to use with a upd socket from an 
repl.  ie. 

  (require local/r6rs/libraries 

the r6rs bytevectors work with the socket but list
processing doesn't work, since the libraries need
mutable pairs and the repl is making immutable

  $ mzscheme 
  Welcome to MzScheme v3.99.0.17 [3m], Copyright (c) 2004-2008 PLT Scheme Inc.
  > (require rnrs/lists-6)
  > (filter even? (list 1 2 3 4 5))
  mcar: expects argument of type <mutable-pair>; given (1 2 3 4 5)

is there a switch i can give mzscheme to make
it generate mlists?  (ie. to make an r6rs + 
udp repl?)


> The thing is that (PLT) Scheme is way more flexible than other
> languages, which makes `emptiness' a questionable concept.  My version
> was empty to an extreme, for example, the equivalent example using
> prefixes as show in:
>>  (perhaps something along the lines of:
>>  http://haskell.org/onlinereport/modules.html#sect5.3.2)

thanks, i have managed to learn why 

  (module x (only-in scheme/base) ...)

is not much use, all of the semi-opaque #% 
infrastructure disappears.  and of course
i recognize plt modules are obviously more 
flexible than haskell etc. but hadn't realized
some of the implications, it does seem to make 
avoiding simple name collisions with 
scheme/base rather tricky?  (i mentioned
the haskell example because the prelude
is also slightly anti-symetrical to ordinary
module use since it is implicit, and you 
need to add a line to make it go away.  also,
i was hoping for an 'only-in' solution instead
of an 'all-except' solution because i already
had an 'only-in' list of all the required 
names from the r6rs variants import list).

btw. the empty variant i had turned out to be
of no use because it interacted badly with 
syntax in a way i did not understand (libraries
would build but could not be used because #%app
didn't exist as a 'syntax transformer'.)  
writing an scheme/empty base language module 
that has all of the required infrastructure 
to write programs & libraries using define/lambda & 
define-syntax/syntax-rules seems non-obvious, 
to an 'outsider' at least.

> uses many `#%app's etc -- and if you want to give them new names you
> can, but it makes the code much more verbose:
>   (module x2 "empty.ss"
>     (#%require (only scheme/base require only-in prefix-in))
>     (require (prefix-in scheme.
>                         (only-in scheme
>                                  #%app #%datum provide define lambda + printf)))
>     (scheme.provide succ)
>     (scheme.define succ
>       (scheme.lambda (n) (scheme.#%app scheme.+ n (scheme.#%datum . 1))))
>     (scheme.#%app scheme.printf (scheme.#%datum . ">>> ~s\n")
>                   (scheme.#%app succ (scheme.#%datum . 7))))
>>  (also, one could hopefully write a lot of scheme without
>>  encountering  #%require #%app #%top #%datum and
>>  #%module-begin.)
> Not really -- but they appear implicitly which is why you usually
> don't care about them.  They're really useful when you want to change
> the semantics of the language in a very fundamental way.

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