module dip2a;
%/* Functions for converting distributive forms into prefix forms*/
%/*Authors: R. Gebauer, A. C. Hearn, H. Kredel*/
expr procedure dip2a u;
% /* Returns prefix equivalent of distributive polynomial u*/
if dipzero!? u then 0 else dipreplus dip2a1 u;
expr procedure dip2a1 u;
if dipzero!? u then nil
else ((if bcminus!? x then list('minus,dipretimes(bc2a bcneg x . y))
else dipretimes(bc2a x . y))
where x = diplbc u, y = expvec2a dipevlmon u)
. dip2a1 dipmred u;
expr procedure dipreplus u;
if atom u then u else if null cdr u then car u else 'plus . u;
expr procedure dipretimes u;
% /* U is a list of prefix expressions the first of which is a number.
% Result is prefix representation for their product*/
if car u = 1 then if cdr u then dipretimes cdr u else 1
else if null cdr u then car u
else 'times . u;
endmodule;
end;