#+TITLE: Where next for guile-prescheme?

* TODO guile repl integration

Currently the "prescheme" language definition is just scheme with a different
default environment (aka. the "prelude", the stuff that's imported by default).

In the Guile REPL you can =,L prescheme= to switch language, but it's not very
useful because you stay in the guile-user module, which is Guile's default
environment, not Pre-Scheme's!

You can create a Pre-Scheme module and switch into it with some effort:

#+BEGIN_SRC scheme
(use-modules (system base language))
(set-module-name! (default-environment 'prescheme) '(prescheme-user))
,module prescheme-user
,language prescheme
#+END_SRC

We need to make the process of "give me a Pre-Scheme REPL" easier.  Maybe just
ship a REPL launcher script which starts up in Pre-Scheme instead of Guile?

* TODO script to build each module

We can use ~guile compile~ to get useful warnings:

#+BEGIN_SRC shell
find -name '*.scm' | xargs -n1 guild compile -W3 -O0 | grep -v '^wrote'
#+END_SRC

* TODO start porting ps-compiler

Above is just the emulation layer.  The real work is the ps-compiler itself,
which is written in Scheme 48 (and also Common Lisp apparently).  This will
involve:

 - rewrite s48 interfaces as guile modules
 - rewrite code using records to use Guile's (or emulate s48?)
 - rewrite macros from explicit renaming to syntax-case
 - ... and many more unforeseen challenges...

* TODO prepare some compatibility tests

We need to find collect all the "real-world" Pre-Scheme we can get our hands on,
and test that our Guile Pre-Scheme produces identical output to Scheme 48
Pre-Scheme.

Exhibit A is the "hello world" from the manual:

#+BEGIN_SRC scheme
;; https://thintz.com/resources/prescheme-documentation#Example-Pre_002dScheme-compiler-usage
(define (main argc argv)
  (if (= argc 2)
      (let ((out (current-output-port)))
        (write-string "Hello, world, " out)
        (write-string (vector-ref argv 1) out)
        (write-char #\! out)
        (newline out)
        0)
      (let ((out (current-error-port)))
        (write-string "Usage: " out)
        (write-string (vector-ref argv 0) out)
        (write-string " <user>" out)
        (newline out)
        (write-string "  Greets the world & <user>." out)
        (newline out)
        -1)))
#+END_SRC

A bunch of tests are included in scheme48-1.9.2/ps-compiler/prescheme/test.
Nice!

* TODO write more TODOs