[erlang-questions] Scheme on the Erlang VM

[Marc Feeley]

On 4-Jun-07, at 3:03 PM, Luke Gorrie wrote:

> "Philip Robinson" <chlorophil@REDACTED> writes:
>
>> On 6/2/07, Joel Reymont <joelr1@REDACTED> wrote:
>>>
>>> What about Scheme on the Erlang VM?
>>
>> I would *love* a Scheme/Lisp on the Erlang VM.
>
> For a toy starting point see 'lersp' in the Jungerl.
>
> The most fun bit of writing a Scheme interpreter IMO is to write
> things like lersp/priv/core-macs.ler i.e. to implement 'let', 'case',
> 'if', etc from a small kernel.
>
> Core Erlang would probably make a nice target language for a Scheme
> dialect.

I just couldn't resist the challenge and wrote a prototype Scheme to  
Erlang compiler (named Stoe of course) that is based on the front-end  
of the Gambit-C Scheme compiler.  The code is attached below.  It is  
just a prototype and it only handles a subset of Scheme, but it could  
be the starting point for a more complete Scheme to Erlang compiler.   
Stoe supports some of the Termite language and mutation of local  
variables.  Here's a sample usage:

% cat test.scm
(define (fib n)
   (if (< n 2) 1 (+ (fib (- n 1)) (fib (- n 2)))))

(define (fact n)
   (if (< n 2) 1 (* n (fact (- n 1)))))

(define (iota n)
   (iota-2 n '()))

(define (iota-2 i lst)
   (if (> i 0)
       (iota-2 (- i 1) (cons i lst))
       lst))

(define (tally)
   (let ((sum 0))
     (lambda (x)
       (set! sum (+ sum x))
       sum)))

(define (process n dest)
   (lambda () (! dest (map (?) (iota n)))))

(define (main)
   (let ((a (spawn (process 10 (self))))
         (b (spawn (process 10 (self))))
         (t1 (tally))
         (t2 (tally)))
     (! a fib)
     (! b fact)
     (map t1 (?))
     (map t2 (?))
     (list (t1 0) (t2 0))))
% gsc -i stoe.scm test.scm
% cat test.erl
-module(test).
-export([fib/1,fact/1,iota/1,iota@REDACTED@2/2,tally/0,process/2,main/0]).

fib(N) ->
   if (N < 2) -> 1; true -> (fib((N - 1)) + fib((N - 2))) end.

fact(N) ->
   if (N < 2) -> 1; true -> (N * fact((N - 1))) end.

iota(N) ->
   iota@REDACTED@2(N,[]).

iota@REDACTED@2(I,Lst) ->
   if (I > 0) -> iota@REDACTED@2((I - 1),[I|Lst]); true -> Lst end.

tally() ->
   Sum = schemelib:box(0),
   fun (X) -> schemelib:setbox(Sum,(schemelib:unbox(Sum) + X)),
     schemelib:unbox(Sum) end.

process(N,Dest) ->
   fun () -> (Dest ! lists:map(receive Tmp_1 -> Tmp_1 end,iota(N))) end.

main() ->
   {T2,T1,B,A} = {tally(),tally(),spawn(process(10,self())),spawn 
(process(10,self()))},
   (A ! fun fib/1),
   (B ! fun fact/1),
   lists:map(T1,receive Tmp_2 -> Tmp_2 end),
   lists:map(T2,receive Tmp_3 -> Tmp_3 end),
   [T1(0),T2(0)].

% erl
Eshell V5.5.4  (abort with ^G)
1> c(schemelib.erl).
{ok,schemelib}
2> c(test.erl).
{ok,test}
3> test:main().
[4037913,231]


Marc

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