[Proposal] Add validation messages to Specs

lib/norm.ex

@@ -150,6 +150,10 @@ defmodule Norm do
     Spec.build(predicate)
   end
 
+  defmacro spec(predicate, message) do
+    Spec.build(predicate, message)
+  end
+
   @doc ~S"""
   Creates a re-usable schema. Schema's are open which means that all keys are
   optional and any non-specified keys are passed through without being conformed.

lib/norm/conformer.ex

@@ -3,6 +3,21 @@ defmodule Norm.Conformer do
   # This module provides an api for conforming values and a protocol for
   # conformable types
 
+  def conform(specs, input) when is_list(specs) do
+    Enum.reduce(specs, {}, fn s, acc ->
+      case acc do
+        {} ->
+          Norm.Conformer.Conformable.conform(s, input, [])
+
+        {:ok, _} ->
+          Norm.Conformer.Conformable.conform(s, input, [])
+
+        {:error, e} ->
+          {:error, e}
+      end
+    end)
+  end
+
   def conform(spec, input) do
     Norm.Conformer.Conformable.conform(spec, input, [])
   end
@@ -15,8 +30,12 @@ defmodule Norm.Conformer do
     |> update_in([:error], &List.flatten(&1))
   end
 
-  def error(path, input, msg) do
-    %{path: path, input: input, spec: msg}
+  def error(path, input, spec_msg) do
+    %{path: path, input: input, spec: spec_msg}
+  end
+
+  def error(path, input, spec_msg, validation_msg) do
+    %{path: path, input: input, spec: spec_msg, message: validation_msg}
   end
 
   def error_to_msg(%{path: path, input: input, spec: msg}) do

lib/norm/core/spec.ex

@@ -9,7 +9,15 @@ defmodule Norm.Core.Spec do
     Or
   }
 
-  defstruct predicate: nil, generator: nil, f: nil
+  defstruct predicate: nil, generator: nil, f: nil, message: nil
+
+  def build(quoted, message) do
+    built_spec = build(quoted)
+
+    quote do
+      %Spec{unquote(built_spec) | message: unquote(message)}
+    end
+  end
 
   def build({:or, _, [left, right]}) do
     l = build(left)
@@ -131,6 +139,19 @@ defmodule Norm.Core.Spec do
   end
 
   defimpl Norm.Conformer.Conformable do
+    def conform(%{f: f, predicate: pred, message: msg}, input, path) do
+      case f.(input) do
+        true ->
+          {:ok, input}
+
+        false ->
+          {:error, [Norm.Conformer.error(path, input, pred, msg)]}
+
+        _ ->
+          raise ArgumentError, "Predicates must return a boolean value"
+      end
+    end
+
     def conform(%{f: f, predicate: pred}, input, path) do
       case f.(input) do
         true ->

test/norm/core/spec_test.exs

@@ -7,6 +7,40 @@ defmodule Norm.Core.SpecTest do
     def match?(x, given), do: x == given
   end
 
+  describe "WIP - spec/2" do
+    test "WIP - can include validation messages" do
+      is_binary_spec = spec(is_binary(), "is not binary")
+
+      {:error, [error]} = conform(1, is_binary_spec)
+
+      assert error.message == "is not binary"
+    end
+
+    test "WIP - can chain specs and their validation messages" do
+      # NOTE: This isn't really a concern of the Spec module but I want to keep things centralized for this POC
+      is_string_spec = [
+        spec(is_binary(), "is not binary"),
+        spec(&(String.length(&1) > 1), "must have more than 2 characters")
+      ]
+
+      {:error, [error]} = conform("", is_string_spec)
+
+      assert error.message == "must have more than 2 characters"
+    end
+
+    test "WIP - chained specs fail fast to not invoke following specs" do
+      # NOTE: This isn't really a concern of the Spec module but I want to keep things centralized for this POC
+      really_bad_spec = [
+        spec(&(&1 && false), "I didn't like that"),
+        spec(&(&1 && raise ""), "I really won't like this")
+      ]
+
+      {:error, [error]} = conform("", really_bad_spec)
+
+      assert error.message == "I didn't like that"
+    end
+  end
+
   describe "spec/1" do
     test "can compose specs with 'and'" do
       hex = spec(is_binary() and (&String.starts_with?(&1, "#")))