Allow top-level function expressions

lib/ahem/lexer.rb

@@ -174,6 +174,13 @@ class Lexer
     end
   end
 
+  def peek
+    position = @position
+    token = get_token
+    @position = position
+    token
+  end
+
   def scan_all
     tokens = Array.new
     until at_end

lib/ahem/parser.rb

@@ -18,18 +18,27 @@ class Parser
     elsif @current_token.type == TokenKinds::LET
       variable_declaration
     elsif @current_token.type == TokenKinds::FUNCTION
-      function_definition
+      next_token = @lexer.peek
+      if next_token && next_token.type == TokenKinds::IDENTIFIER
+				function_definition
+      else
+				expression_statement
+      end
     elsif @current_token.type == TokenKinds::CLASS
       class_definition
     elsif @current_token.type == TokenKinds::FOR
       for_loop
     else
-      expr = expression
-      eat(TokenKinds::SEMICOLON)
-      expr
+			expression_statement
     end
   end
 
+	def expression_statement
+    expr = expression
+    eat(TokenKinds::SEMICOLON)
+    return expr
+	end
+
   def variable_declaration
     eat(TokenKinds::LET)
     name = identifier

spec/parser_spec.rb

@@ -402,4 +402,54 @@ RSpec.describe Parser do
       ]
     )
   end
+
+  it 'allows returning an anonymous function from another function' do
+    expect(parse('function outer() { function() { print("Hello world"); }; }')).to eq(
+      [
+        AST::FunctionDefinition.new(
+          AST::Identifier.new('outer'),
+          [],
+          AST::Block.new(
+            [
+              AST::FunctionDefinition.new(
+                nil,
+                [],
+                AST::Block.new(
+                  [
+                    AST::FunctionCall.new(
+                      AST::Identifier.new('print'),
+                      [
+                        AST::String.new('Hello world')
+                      ]
+                    )
+                  ]
+                )
+              )
+            ]
+          )
+        )
+      ]
+    )
+  end
+
+	it 'allows toplevel function expressions' do
+    expect(parse('function() { print("Hello world"); };')).to eq(
+      [
+        AST::FunctionDefinition.new(
+          nil,
+          [],
+          AST::Block.new(
+            [
+              AST::FunctionCall.new(
+                AST::Identifier.new('print'),
+                [
+                  AST::String.new('Hello world')
+                ]
+              )
+            ]
+          )
+        )
+      ]
+    )
+	end
 end