what's wrong ?

[prieur@smart.irit.fr (Pascal PRIEUR)]

Hi,

i 'm working with centaur-2.0.
I would like to write a function, which calculates a random number, and i
want to use it in my typol's program. But i 'mnot able to realize it.

this is my typol stuff :

taille(lref |- litteralint n) & 
choisir_valeur(litteralint n,litteralint x) &
recherche_acteur( lref,lref |- litteralint "1", litteralint x -> 
				identite(litteralint m,FILE,CONT,link,comp) 
				: message)
---------------------------------------------------------------------
|- lref -> identite(litteralint m,FILE,CONT,link,comp) + message ;

this typol's rule seeks one element of the list lref.
taille calculates the length of lref, and lref is a list.
my ``litteralint'' is implemented with metal as a STRING.
choisir_valeur calculates a random number between 1 and lenght(lref)+1
taille and recherche_acteur are OK, but when i ``step'' with the debugger to
choisir_valeur, i always had errors, or backtrack step !!
error is like this one :
Error: err-vtp-protocol: type error in _g2286 =.. [1, _g2272, _g2276, _g2280] 
Warning: ** MM-error : : Timeout occurred 


here they are my prolog functions :
plasmafunc$add1('$Plasma$litteralint'(A),'$Plasma$litteralint'(B)) :- 
			$lispfun_atom(addition,[A],B).

plasmafunc$choisir_valeur('$Plasma$litteralint'(X),'$Plasma$litteralint'(Y)):- 
				$lispfun_atom(tirerausort,[X],Y).

and my lisp functions :

(de addition( A )
(+ (implode (explode A)) 1))

(de tirerausort( A ) 
(srandom) (random 1 (+ (implode (explode A)) 1)))

i use implode & explode because i receive atoms, in lisp and to realize addition, i
need numbers.

i would like to know what's wrong, with lisp or prolog or typol, ...

thanks in advance.