Decisiones anidadas , Prolog

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objeto :- write('{'), read(X), (X='atributo'->atributo;
                                write('')), write('}').
atributo:- cadena, write(':'), valor,a1.
a1 :- read(X), (X='atributo'->write(','),atributo;
                    X='fin'->write('')).
valor :- read(X), (X='numero'->numero;
                    X='cadena'->cadena;
                    X='metodo'->metodo;                    
                    X='objeto'->objeto).
metodo:- write('"function() {'),instruccion,write('return '), read(X), write(X), write(';}"').

instruccion:- read(X), (X='asignacion'->asignacion;
                    X='decision'->decision;
                    X='fin'->write('')).
decision:- write('if ('),read(X),write(X),write(')'),verdadero, falso.
verdadero:- write('{'),instruccion,write('}').
falso:- write('else{'),instruccion,write('}').
asignacion:- read(X),write(X),write('='),read(Y),write(Y),write(';'),instruccion.                    
cadena:- write('"'),read(X),write(X),write('"').
numero:- read(X),write(X).
:- objeto.

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