isan con puro if sin else, Prolog

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objeto :- write('{'),aux1, write('}').
aux1 :- read(X),(X='atributo'->atributo;
                 X='fin'->write('')).
atributo :-cadena, write(':'),valor,aux2.
arreglo :- write('['),aux3, write(']').
aux2 :- read(X),(X='atributo'->write(','),atributo;
                 X='fin'->write('')).
aux3 :- read(X),(X='valor'->valor,aux4;
                 X='fin'->write('')).
aux4 :- read(X),(X='valor'->write(','),valor,aux4;
                 X='fin'->write('')).
cadena :- read(X),write('"'),write(X),write('"').
numero :- read(X),write(X).
valor :-read(T),(T='cadena'->cadena;
                 T='numero'->numero;
                 T='arreglo'->arreglo;
                 T='metodo'->metodo;
                 T='objeto'->objeto).

metodo :- write('"function() {'),instruccion,write('return isan}"').
instruccion :-read(I),(I='asignacion'->asignacion,instruccion;
                       I='decision'->decision,instruccion;
                       I='fin'->write('')).
asignacion :- numero,write('='),numero,write(';').
decision :- write('if ('),condicion,write('){'),instruccion,write('}').
condicion :- numero.
:- objeto.

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