Store function name on the function node

lib/chervil/ast/function.rb

 module Chervil::AST
   class Function
+    attr_reader :name
     attr_reader :params
     attr_reader :body
 
-    def initialize(params, body)
+    def initialize(name, params, body)
+      @name = name
       @params = params
       @body = body
     end
 
     def ==(other)
-      @params == other.params && @body == other.body
+      @name == other.name && @params == other.params && @body == other.body
     end
 
     def evaluate(env)
     end
 
     def to_s
-      "<function>"
+      "<function: #{@name.name}(#{@params.map(&:name).join(' ')})>"
     end
   end
 end

lib/chervil/parser.rb

 
         eat(:rparen)
 
-        AST::Definition.new(name, AST::Function.new(params, body))
+        AST::Definition.new(name, AST::Function.new(name, params, body))
       end
     end
 

spec/ast/function_spec.rb

 module Chervil
   RSpec.describe AST::Definition do
     it 'evaluates its body with its arguments when called' do
-      env = Env.new
       expect(
         AST::Function.new(
+          AST::Identifier.new("square"),
           [
             AST::Identifier.new("x")
           ],

spec/parser_spec.rb

         AST::Definition.new(
           AST::Identifier.new("square"),
           AST::Function.new(
+            AST::Identifier.new("square"),
             [
               AST::Identifier.new("x")
             ],