Allow calling anonymous functions directly

lib/ahem/ast/function_call.rb

@@ -13,7 +13,12 @@ class AST::FunctionCall
 
   def execute(env)
     env = Environment.new(env)
-    function = env.get(@function.name)
+
+    function = if @function.is_a?(AST::Identifier)
+      env.get(@function.name)
+    elsif @function.is_a?(AST::FunctionDefinition)
+      @function
+    end
 
     if function.is_a?(AST::FunctionDefinition)
       if @arguments.size != function.parameters.size

spec/ast/function_call_spec.rb

@@ -184,4 +184,20 @@ RSpec.describe AST::FunctionCall do
 
     expect(result).to eq(6)
   end
+
+  it 'allows calling an anonymous function directly' do
+    result = AST::FunctionCall.new(
+      AST::FunctionDefinition.new(
+        nil,
+        [],
+        AST::Block.new(
+          [
+            AST::Number.new(5.0)
+          ]
+        )
+      ),
+      []
+    ).execute(Environment.new)
+    expect(result).to eq(5.0)
+  end
 end