feat(calc): supports function definition and evaluation

6 files changed, 99 insertions, 13 deletions

diff --git a/example/input.txt b/example/input.txt
index 9c49d56..bd668e0 100644
--- a/example/input.txt
+++ b/example/input.txt
@@ -1,9 +1,9 @@
 a = 10.05;; b = .95 
 (a + b) * 10 / 2
 
-x = 2_0
-y = 2!
-z = y/2 
-10 + 4(z / y)(x / 4)
-
-x^(-y)
+f: x = x + 1
+x = 2
+# is 24 + 1 = 25
+f(24) 
+# must be 10
+x(5) 
diff --git a/lib/elixir_math_parser.ex b/lib/elixir_math_parser.ex
index 286829e..b7f080c 100644
--- a/lib/elixir_math_parser.ex
+++ b/lib/elixir_math_parser.ex
@@ -5,6 +5,7 @@ defmodule ElixirMathParser do
   alias ElixirMathParser.Math.Rational
   alias ElixirMathParser.Math.Calc
   alias ElixirMathParser.Math.Conversion
+  alias ElixirMathParser.Math.Function
 
   defp reduce_to_value({:int, _line, value}, _state) do
     {:ok, Rational.new(value)}
@@ -76,11 +77,35 @@ defmodule ElixirMathParser do
     end
   end
 
+  defp reduce_to_value({:eval_func, {:var, line, var}, params}, state) do
+    if !Map.has_key?(state, var) do
+      {:error, line, "function " <> to_string(var) <> " not found"}
+    else
+      v = state[var]
+
+      # check if the mult is implicit
+      if Rational.is_rational(v) do
+        [head | _] = params
+        reduce_to_value({:mul_op, {:var, line, var}, head}, state)
+      else
+        params = Enum.map(params, fn v -> with {:ok, v} <- reduce_to_value(v, state), do: v end)
+
+        with {:ok, v} <- state[var] |> Function.eval(params) do
+          {:ok, v}
+        else
+          {:error, reason} -> {:error, line, reason}
+          {:error, line, reason} -> {:error, line, reason}
+        end
+      end
+    end
+  end
+
   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}))
     else
       {:error, reason} -> {:error, line, reason}
+      {:error, line, reason} -> {:error, line, reason}
     end
   end
 
@@ -92,6 +117,21 @@ defmodule ElixirMathParser do
     end
   end
 
+  defp evaluate_tree([{:assign_func, {:var, _line, name}, vars, expr} | tail], state) do
+    fun =
+      Function.new(
+        fn params, given ->
+          state =
+            Enum.reduce(given, state, fn {v, id}, acc -> Map.merge(acc, %{params[id] => v}) end)
+
+          reduce_to_value(expr, state)
+        end,
+        Enum.map(vars, fn {:var, _line, name} -> name end)
+      )
+
+    evaluate_tree(tail, Map.merge(state, %{name => fun}))
+  end
+
   defp evaluate_tree([], state) do
     {:ok, state}
   end
diff --git a/lib/math/function.ex b/lib/math/function.ex
new file mode 100644
index 0000000..2acf2c4
--- /dev/null
+++ b/lib/math/function.ex
@@ -0,0 +1,28 @@
+defmodule ElixirMathParser.Math.Function do
+  alias ElixirMathParser.Math.Function
+
+  defstruct relation: nil, parameters: %{}
+
+  def is_function(val) when is_map(val) and is_map_key(val, :__struct__) and is_struct(val),
+    do: :erlang.map_get(:__struct__, val) == __MODULE__
+
+  def new(relation, parameters) do
+    params =
+      Enum.with_index(parameters)
+      |> Enum.reduce(%{}, fn {v, id}, acc -> Map.merge(acc, %{id => v}) end)
+
+    %Function{relation: relation, parameters: params}
+  end
+
+  def eval(fun, parameters) do
+    if Enum.count(parameters) != Enum.count(fun.parameters) do
+      {:error, "wrong count of parameters"}
+    else
+      params =
+        Enum.with_index(parameters)
+        |> Enum.reduce(%{}, fn {v, id}, acc -> Map.merge(acc, %{v => id}) end)
+
+      fun.relation.(fun.parameters, params)
+    end
+  end
+end
diff --git a/lib/math/rational.ex b/lib/math/rational.ex
index c3d94c9..e788883 100644
--- a/lib/math/rational.ex
+++ b/lib/math/rational.ex
@@ -83,9 +83,8 @@ defmodule ElixirMathParser.Math.Rational do
   iex> Rational.is_rational("My quick brown fox")
   false
   """
-  defguard is_rational(val)
-           when is_map(val) and is_map_key(val, :__struct__) and is_struct(val) and
-                  :erlang.map_get(:__struct__, val) == __MODULE__
+  def is_rational(val) when is_map(val) and is_map_key(val, :__struct__) and is_struct(val),
+    do: :erlang.map_get(:__struct__, val) == __MODULE__
 
   @doc """
   Creates a new Rational number.
diff --git a/src/elixir_math_parser.yrl b/src/elixir_math_parser.yrl
index 635ebd3..a48b57b 100644
--- a/src/elixir_math_parser.yrl
+++ b/src/elixir_math_parser.yrl
@@ -4,15 +4,21 @@ Nonterminals
   statements
   expr
   exprs
+  % function specific
+  vars params
 .
 
 Terminals
   int float
   var
   break
+  % eval
   '+' '-' '*' '/' '!' '^'
-  '='
   '(' ')'
+  % assign
+  '='
+  % function specific
+  ':' ','
 .
 
 Rootsymbol
@@ -37,13 +43,22 @@ statements -> break : [].
 
 statement -> var '=' exprs : {assign, '$1', '$3'}.
 statement -> exprs : {eval, '$1'}.
+statement -> var ':' vars '=' exprs : {assign_func, '$1', '$3', '$5'}.
+
+vars -> var : ['$1'].
+vars -> var ',' vars : ['$1' | '$3'].
 
-exprs -> expr       : '$1'.
+exprs -> expr : '$1'.
 exprs -> expr exprs : {mul_op, '$1', '$2'}.
 
+params -> expr : ['$1'].
+params -> expr ',' : ['$1'].
+params -> expr ',' params : ['$1' | '$3'].
+
 expr -> int : unwrap('$1').
 expr -> float : unwrap('$1').
 expr -> var : '$1'.
+
 expr -> exprs '+' exprs : {add_op, '$1', '$3'}.
 expr -> exprs '-' exprs : {sub_op, '$1', '$3'}.
 expr -> exprs '*' exprs : {mul_op, '$1', '$3'}.
@@ -53,6 +68,8 @@ expr -> exprs '^' exprs : {exp_op, '$1', '$3'}.
 expr -> '(' exprs ')' : '$2'.
 expr -> '-' exprs : {sub_op, {int, 0, 0}, '$2'}.
 
+expr -> var '(' params ')' : {eval_func, '$1', '$3'}.
+
 Erlang code.
 
 % 95 is the unicode of "_"
diff --git a/src/elixir_math_parser_lexer.xrl b/src/elixir_math_parser_lexer.xrl
index 4073958..fdb661f 100644
--- a/src/elixir_math_parser_lexer.xrl
+++ b/src/elixir_math_parser_lexer.xrl
@@ -4,7 +4,7 @@ FLOAT      = [0-9_]*\.[0-9]+
 NAME       = [a-zA-Z_][a-zA-Z0-9_]*
 WHITESPACE = [\s\t\r]
 COMMENT    = #[^\n]*\n?
-BREAK      = [\n;;]
+BREAK      = [\n;;]+
 
 Rules.
 \+            : {token, {'+',  TokenLine}}.
@@ -16,7 +16,9 @@ Rules.
 \)            : {token, {')',  TokenLine}}.
 !             : {token, {'!',  TokenLine}}.
 \^            : {token, {'^',  TokenLine}}.
-{BREAK}+      : {token, {break,  TokenLine}}.
+\:            : {token, {':', TokenLine}}.
+,             : {token, {',', TokenLine}}.
+{BREAK}       : {token, {break,  TokenLine}}.
 {NAME}        : {token, {var, TokenLine, TokenChars}}.
 {FLOAT}       : {token, {float, TokenLine, TokenChars}}.
 {INT}         : {token, {int,  TokenLine, TokenChars}}.