@@ -2,7 +2,7 @@ % info go to <URL:http://en.wikipedia.org/wiki/Shunting_yard_algorithm>. -module(calc). --export([parse/1, evaluate/1, stringify/1, compile/1, simulate/1, simplify/1]). +-export([parse/1, evaluate/1, stringify/1, compile/1, simulate/1, optimize/1]). parse(String) -> parse(tokenize(String), [], []). @@ -83,54 +83,54 @@ simulate([Oper|Instructions], [Stack0|[Stack1|Stack]]) -> divide -> simulate(Instructions, [Stack1 / Stack0|Stack]) end. -simplify({num, Num}) -> {num, Num}; -simplify({add, Exp0, {uminus, Exp1}}) -> simplify({subtract, simplify(Exp0), simplify(Exp1)}); -simplify({subtract, Exp0, {uminus, Exp1}}) -> simplify({add, simplify(Exp0), simplify(Exp1)}); -simplify({uminus, Exp}) -> - Sexp = simplify(Exp), - case Sexp of +optimize({num, Num}) -> {num, Num}; +optimize({add, Exp0, {uminus, Exp1}}) -> optimize({subtract, optimize(Exp0), optimize(Exp1)}); +optimize({subtract, Exp0, {uminus, Exp1}}) -> optimize({add, optimize(Exp0), optimize(Exp1)}); +optimize({uminus, Exp}) -> + Oexp = optimize(Exp), + case Oexp of {uminus, NestedExp} -> NestedExp; - _ -> {uminus, Sexp} + _ -> {uminus, Oexp} end; -simplify({add, Exp0, Exp1}) -> - Sexp0 = simplify(Exp0), - Sexp1 = simplify(Exp1), +optimize({add, Exp0, Exp1}) -> + Oexp0 = optimize(Exp0), + Oexp1 = optimize(Exp1), if - Sexp0 == {num, 0} -> Sexp1; - Sexp1 == {num, 0} -> Sexp0; - true -> {add, Sexp0, Sexp1} + Oexp0 == {num, 0} -> Oexp1; + Oexp1 == {num, 0} -> Oexp0; + true -> {add, Oexp0, Oexp1} end; -simplify({subtract, Exp0, Exp1}) -> - Sexp0 = simplify(Exp0), - Sexp1 = simplify(Exp1), +optimize({subtract, Exp0, Exp1}) -> + Oexp0 = optimize(Exp0), + Oexp1 = optimize(Exp1), if - Sexp0 == {num, 0} -> {uminus, Sexp1}; - Sexp1 == {num, 0} -> Sexp0; - Sexp0 == Sexp1 -> {num, 0}; - true -> {subtract, Sexp0, Sexp1} + Oexp0 == {num, 0} -> {uminus, Oexp1}; + Oexp1 == {num, 0} -> Oexp0; + Oexp0 == Oexp1 -> {num, 0}; + true -> {subtract, Oexp0, Oexp1} end; -simplify({multiply, Exp0, Exp1}) -> - Sexp0 = simplify(Exp0), - Sexp1 = simplify(Exp1), +optimize({multiply, Exp0, Exp1}) -> + Oexp0 = optimize(Exp0), + Oexp1 = optimize(Exp1), if - Sexp0 == {num, 0}; Sexp1 == {num, 0} -> {num, 0}; - Sexp0 == {num, 1} -> Sexp1; - Sexp1 == {num, 1} -> Sexp0; - true -> {multiply, Sexp0, Sexp1} + Oexp0 == {num, 0}; Oexp1 == {num, 0} -> {num, 0}; + Oexp0 == {num, 1} -> Oexp1; + Oexp1 == {num, 1} -> Oexp0; + true -> {multiply, Oexp0, Oexp1} end; -simplify({divide, Exp0, Exp1}) -> - Sexp0 = simplify(Exp0), - Sexp1 = simplify(Exp1), +optimize({divide, Exp0, Exp1}) -> + Oexp0 = optimize(Exp0), + Oexp1 = optimize(Exp1), if - Sexp0 == Sexp1 -> {num, 1}; - Sexp0 == {num, 0} -> {num, 0}; - Sexp1 == {num, 1} -> Sexp0; - true -> {divide, Sexp0, Sexp1} + Oexp0 == Oexp1 -> {num, 1}; + Oexp0 == {num, 0} -> {num, 0}; + Oexp1 == {num, 1} -> Oexp0; + true -> {divide, Oexp0, Oexp1} end; -simplify({Oper, Exp}) -> - {Oper, simplify(Exp)}; -simplify({Oper, Exp0, Exp1}) -> - {Oper, simplify(Exp0), simplify(Exp1)}. +optimize({Oper, Exp}) -> + {Oper, optimize(Exp)}; +optimize({Oper, Exp0, Exp1}) -> + {Oper, optimize(Exp0), optimize(Exp1)}. tokenize([]) -> []; tokenize([H|T]) -> chapter3/calc.erl 48033a62a21a597720a20dc6aaf53b31dd90f53f John Parker jparker@urgetopunt.com http://github.com/jparker/erlang_programming/commit/568dd7ac88a465529bd3e9d1760d4ee743b87a33 568dd7ac88a465529bd3e9d1760d4ee743b87a33 2009-10-09T06:30:22-07:00 2009-10-09T06:30:22-07:00 Renamed function simplify() to optimize() d45f76da94ab65d29fa5bc33609bff404a93111c John Parker jparker@urgetopunt.com