4 files changed, 31 insertions, 3 deletions
diff --git a/example/input.txt b/example/input.txt
index 7efcb9c..8cb02c5 100644
--- a/example/input.txt
+++ b/example/input.txt
@@ -5,3 +5,5 @@ x = 20
 y = 2!
 z = y/2 
 10 + 4(z / y)(x / 4)
+
+x^(0-y)
diff --git a/lib/elixir_math_parser.ex b/lib/elixir_math_parser.ex
index 863ecd8..b5e99bd 100644
--- a/lib/elixir_math_parser.ex
+++ b/lib/elixir_math_parser.ex
@@ -57,9 +57,32 @@ defmodule ElixirMathParser do
     end
   end
 
+  defp reduce_to_value({:exp_op, lhs, rhs}, state) do
+    with {:ok, op1} <- reduce_to_value(lhs, state),
+         {:ok, op2} <- reduce_to_value(rhs, state) do
+      if Ratio.denominator(op2) == 1 do
+        {:ok, expo(op1, Ratio.numerator(op2), 1)}
+      else
+        {:error, "unsupported operation"}
+      end
+    end
+  end
+
+  #  Functions for maths
+
   defp factor(n, acc) when n > 0, do: factor(n - 1, acc * n)
   defp factor(0, acc), do: acc
 
+  defp expo(value, exponent, acc) when exponent != 0 do
+    if exponent > 0 do
+      expo(value, exponent - 1, acc * value)
+    else
+      expo(value, exponent + 1, acc / value)
+    end
+  end
+
+  defp expo(_value, 0, acc), do: acc
+
   defp evaluate_tree([{:assign, {:var, line, lhs}, rhs} | tail], state) do
     with {:ok, val} <- reduce_to_value(rhs, state) do
       evaluate_tree(tail, Map.merge(state, %{lhs => val}))
diff --git a/src/elixir_math_parser.yrl b/src/elixir_math_parser.yrl
index 0808683..006c768 100644
--- a/src/elixir_math_parser.yrl
+++ b/src/elixir_math_parser.yrl
@@ -10,7 +10,7 @@ Terminals
   int
   var
   break
-  '+' '-' '*' '/' '!'
+  '+' '-' '*' '/' '!' '^'
   '='
   '(' ')'
 .
@@ -25,7 +25,8 @@ Left 300 '-'.
 Left 400 '*'.
 Left 400 '/'.
 Right 500 '!'.
-Left 600 '('.
+Left 600 '^'.
+Left 700 '('.
 
 root -> statements : '$1'.
 
@@ -46,8 +47,9 @@ expr -> exprs '+' exprs : {add_op, '$1', '$3'}.
 expr -> exprs '-' exprs : {sub_op, '$1', '$3'}.
 expr -> exprs '*' exprs : {mul_op, '$1', '$3'}.
 expr -> exprs '/' exprs : {div_op, '$1', '$3'}.
-expr -> '(' exprs ')' : '$2'.
 expr -> expr '!' : {factor_op, '$1'}.
+expr -> exprs '^' exprs : {exp_op, '$1', '$3'}.
+expr -> '(' exprs ')' : '$2'.
 
 Erlang code.
 
diff --git a/src/elixir_math_parser_lexer.xrl b/src/elixir_math_parser_lexer.xrl
index 5bdcbef..c29416e 100644
--- a/src/elixir_math_parser_lexer.xrl
+++ b/src/elixir_math_parser_lexer.xrl
@@ -14,6 +14,7 @@ Rules.
 \(            : {token, {'(',  TokenLine}}.
 \)            : {token, {')',  TokenLine}}.
 !             : {token, {'!',  TokenLine}}.
+\^            : {token, {'^',  TokenLine}}.
 {BREAK}+      : {token, {break,  TokenLine}}.
 {NAME}        : {token, {var, TokenLine, TokenChars}}.
 {INT}         : {token, {int,  TokenLine, TokenChars}}.