gistfile1.erl

module(simplification).
-compile([export_all]).

zeroA({add,E,{num,0}}) -> E;
zeroA({add,{num,0},E}) -> E;
zeroA(E) -> E.

mulO({mul,E,{num,1}}) -> E;
mulO({mul,{num,1},E}) -> E;
mulO(E) -> E.

mulZ({mul,_,{num,0}}) -> {num,0};
mulZ({mul,{num,0},_}) -> {num,0};
mulZ(E) -> E.

compose([])-> fun (E) -> E end;
compose([Rule|Rules]) -> 
	fun (E) -> (compose(Rules))(Rule(E)) end.
	
rules() -> [ fun zeroA/1, fun mulO/1, fun mulZ/1].

simp(F,{add,E1,E2}) ->
    F({add,simp(F,E1),simp(F,E2)});
simp(F,{mul,E1,E2}) ->
    F({mul,simp(F,E1),simp(F,E2)});
simp(_F,E) -> E.

simplify(E) -> simp(compose(rules()),E).