@@ -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]). +-export([parse/1, evaluate/1, stringify/1, compile/1, simulate/1, simplify/1]). parse(String) -> parse(tokenize(String), [], []). @@ -60,6 +60,80 @@ stringify({Oper, Exp0, Exp1}) -> divide -> "(" ++ stringify(Exp0) ++ "/" ++ stringify(Exp1) ++ ")" end. +compile(Exp) -> compile(Exp, []). + +compile({num, Num}, Stack) -> + [{push, Num}|Stack]; +compile({Oper, Exp}, Stack) -> + compile(Exp, [Oper|Stack]); +compile({Oper, Exp0, Exp1}, Stack) -> + compile(Exp0, compile(Exp1, [Oper|Stack])). + +simulate(Instructions) -> simulate(Instructions, []). + +simulate([], [Top]) -> + Top; +simulate([{push, Num}|Instructions], Stack) -> + simulate(Instructions, [Num|Stack]); +simulate([uminus|Instructions], [Stack0|Stack]) -> + simulate(Instructions, [-Stack0|Stack]); +simulate([Oper|Instructions], [Stack0|[Stack1|Stack]]) -> + case Oper of + add -> simulate(Instructions, [Stack1 + Stack0|Stack]); + subtract -> simulate(Instructions, [Stack1 - Stack0|Stack]); + multiply -> simulate(Instructions, [Stack1 * Stack0|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 + {uminus, NestedExp} -> NestedExp; + _ -> {uminus, Sexp} + end; +simplify({add, Exp0, Exp1}) -> + Sexp0 = simplify(Exp0), + Sexp1 = simplify(Exp1), + if + Sexp0 == {num, 0} -> Sexp1; + Sexp1 == {num, 0} -> Sexp0; + true -> {add, Sexp0, Sexp1} + end; +simplify({subtract, Exp0, Exp1}) -> + Sexp0 = simplify(Exp0), + Sexp1 = simplify(Exp1), + if + Sexp0 == {num, 0} -> {uminus, Sexp1}; + Sexp1 == {num, 0} -> Sexp0; + Sexp0 == Sexp1 -> {num, 0}; + true -> {subtract, Sexp0, Sexp1} + end; +simplify({multiply, Exp0, Exp1}) -> + Sexp0 = simplify(Exp0), + Sexp1 = simplify(Exp1), + if + Sexp0 == {num, 0}; Sexp1 == {num, 0} -> {num, 0}; + Sexp0 == {num, 1} -> Sexp1; + Sexp1 == {num, 1} -> Sexp0; + true -> {multiply, Sexp0, Sexp1} + end; +simplify({divide, Exp0, Exp1}) -> + Sexp0 = simplify(Exp0), + Sexp1 = simplify(Exp1), + if + Sexp0 == Sexp1 -> {num, 1}; + Sexp0 == {num, 0} -> {num, 0}; + Sexp1 == {num, 1} -> Sexp0; + true -> {divide, Sexp0, Sexp1} + end; +simplify({Oper, Exp}) -> + {Oper, simplify(Exp)}; +simplify({Oper, Exp0, Exp1}) -> + {Oper, simplify(Exp0), simplify(Exp1)}. + tokenize([]) -> []; tokenize([H|T]) -> if chapter3/calc.erl fc1bb07e306a396b804a954f022c6fc32a73c7b4 John Parker jparker@urgetopunt.com http://github.com/jparker/erlang_programming/commit/706baece6670d57706d7587c0d7cbbe40be039b0 706baece6670d57706d7587c0d7cbbe40be039b0 2009-10-08T22:53:25-07:00 2009-10-08T22:53:25-07:00 Implemented compile(), simulate() and simplify() functions 228adab825ca6641db4aa69cc3b8e05f854f20cd John Parker jparker@urgetopunt.com