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  1. -module(prog).
  2. -export([main/0, eval4th/2, tokenize/1]).
  3.  
  4. tokenize(S) ->
  5.   [(fun(T) ->
  6.     case string:to_float(T) of
  7.     {error, _} ->
  8.       case string:to_integer(T) of
  9.       {error, _} -> T;
  10.       {Int, _} -> Int
  11.       end;
  12.     {Float, _} -> Float
  13.     end
  14.   end)(E) || E <- string:tokens(S, " ")].
  15.  
  16. eval4th(Que, []) -> Que;
  17. eval4th(Que, [H|T]) ->
  18.   Q = case H of
  19.   "+" -> ope2items(Que, fun(A, B) -> A + B end);
  20.   "-" -> ope2items(Que, fun(A, B) -> A - B end);
  21.   "*" -> ope2items(Que, fun(A, B) -> A * B end);
  22.   "/" -> ope2items(Que, fun(A, B) -> A / B end);
  23.   "." -> {A, Q0} = pop1item(Que), io:format("~p~n", [A]), Q0;
  24.   N when is_number(N) -> queue:in_r(N, Que);
  25.   _ -> io:format("*** unexpected token [~p] ***~n", [H]), throw({exit, Que})
  26.   end,
  27.   eval4th(Q, T).
  28.  
  29. ope2items(Que, Ope) ->
  30.   {B, A, Q} = pop2items(Que),
  31.   queue:in_r(Ope(A, B), Q).
  32.  
  33. pop2items(Que) ->
  34.   case queue:out(Que) of
  35.   {{value, B}, Q1} ->
  36.     case queue:out(Q1) of
  37.     {{value, A}, Q2} -> {B, A, Q2};
  38.     {empty, _Q2} -> io:format("** empty second **~n", []), throw({exit, Que})
  39.     end;
  40.   {empty, _Q1} -> io:format("** empty first **~n", []), throw({exit, Que})
  41.   end.
  42.  
  43. pop1item(Que) ->
  44.   case queue:out(Que) of
  45.   {{value, A}, Q} -> {A, Q};
  46.   {empty, _Q} -> io:format("** empty top **~n", []), throw({exit, Que})
  47.   end.
  48.  
  49. main() ->
  50.   eval4th(queue:new(), tokenize("3 2 1 + * 1 - 4 / .")).
Success #stdin #stdout 0.19s 23408KB
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2.0
https://ideone.com/GTo0rm
language:
Erlang (erl 21.3.8)
created:
9 years ago
visibility:
public

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