improvement: handle when clauses on anonymous functions

lib/spark/code_helpers.ex

@@ -135,11 +135,23 @@ defmodule Spark.CodeHelpers do
     function = generate_captured_function_caller(fn_name, fn_args, caller)
 
     function_defs =
-      for {:->, _, [args, body]} <- clauses do
-        quote do
-          def unquote(fn_name)(unquote_splicing(args)) do
-            unquote(body)
-          end
+      for clause <- clauses do
+        case clause do
+          {:->, _, [[{:when, _, args_with_clause}], body]} ->
+            args = :lists.droplast(args_with_clause)
+            clause = List.last(args_with_clause)
+            quote do
+              def unquote(fn_name)(unquote_splicing(args)) when unquote(clause) do
+                unquote(body)
+              end
+            end
+
+          {:->, _, [args, body]} ->
+            quote do
+              def unquote(fn_name)(unquote_splicing(args)) do
+                unquote(body)
+              end
+            end
         end
       end
 

test/dsl_test.exs

@@ -45,7 +45,7 @@ defmodule Spark.DslTest do
         use Spark.Test.Contact
 
         contact do
-          contacter(fn message ->
+          contacter(fn message when not is_nil(message) ->
             "Help me Obi-Wan Kenobi: #{message}"
           end)
         end