Experiment - coercion

lib/norm.ex

@@ -26,6 +26,26 @@ defmodule Norm do
     end
   end
 
+  @doc ~S"""
+  Coerces the value based on the specification.
+
+  ## Examples:
+
+      iex> coerce("42", spec(is_integer))
+      42
+      iex> coerce("5.0", spec(is_float))
+      5.0
+      iex> coerce("a", spec(is_binary))
+      "a"
+      iex> coerce("a", spec(is_atom))
+      :a
+      iex> coerce(%{"a" => "123"}, schema(%{a: spec(is_integer)}))
+      %{a: 123}
+  """
+  def coerce(input, spec) do
+    Norm.Coerceable.coerce(spec, input)
+  end
+
   @doc ~S"""
   Verifies that the payload conforms to the specification. A "success tuple"
   is returned that contains either the conformed value or the error explanation.

lib/norm/coerceable.ex

@@ -0,0 +1,84 @@
+defprotocol Norm.Coerceable do
+  @moduledoc false
+
+  def coerce(spec, input)
+end
+
+defimpl Norm.Coerceable, for: Norm.Core.Schema do
+  require Norm
+
+  def coerce(%{specs: specs}, input) when is_map(input) do
+    specs
+    |> Enum.map(fn {key, spec} ->
+      cond do
+        is_atom(key) ->
+          case Enum.find(input, fn {k, v} -> Atom.to_string(key) == k || k == key end) do
+            {k, v} -> {Norm.Coerceable.coerce(Norm.spec(is_atom), k), Norm.Coerceable.coerce(spec, v)}
+          end
+      end
+    end)
+    |> Enum.into(%{})
+  end
+end
+
+defimpl Norm.Coerceable, for: Norm.Core.Spec do
+  def coerce(%{f: f, generator: gen}, input) do
+    sym_to_coercer(gen, input)
+  end
+
+  defp sym_to_coercer(:is_atom, input) do
+    :"#{input}"
+  end
+
+  defp sym_to_coercer(:is_binary, input) do
+    "#{input}"
+  end
+
+  defp sym_to_coercer(:is_bitstring, input) do
+    "#{input}"
+  end
+
+  defp sym_to_coercer(:is_boolean, input) do
+    case input do
+      "true" -> true
+      "false" -> false
+    end
+  end
+
+  defp sym_to_coercer(:is_float, input) do
+    cond do
+      is_binary(input) -> String.to_float(input)
+      is_integer(input) -> input / 1
+    end
+  end
+
+  defp sym_to_coercer(:is_integer, input) do
+    cond do
+      is_binary(input) -> String.to_integer(input)
+      is_float(input) -> round(input)
+    end
+  end
+
+  defp sym_to_coercer(:is_nil, input) do
+    case input do
+      "null" -> nil
+      "nil" -> nil
+    end
+  end
+
+  defp sym_to_coercer(:is_number, input) do
+    cond do
+      is_binary(input) -> String.to_integer(input)
+      is_float(input) -> round(input)
+      is_integer(input) -> input
+    end
+  end
+
+  # defp sym_to_coercer(:is_list, input) do
+  # end
+
+  defp sym_to_coercer(gen, input) do
+    input
+    # default
+  end
+end