fix parsing bug w/no conditional in a for loop

ruby/lib/lox/parser.rb

@@ -68,10 +68,10 @@ module Lox
                       expression_stmt
                     end
 
-      condition = !check?(:SEMICOLON) ? expression : Expr::Literal(true)
+      condition = check?(:SEMICOLON) ? Expr::Literal.new(true) : expression
       consume!(:SEMICOLON, "Expect ';' after loop condition.")
 
-      increment = !check?(:RIGHT_PAREN) ? expression : nil
+      increment = check?(:RIGHT_PAREN) ? nil : expression
       consume!(:RIGHT_PAREN, "Expect ')' after for clauses.")
 
       body = statement

ruby/test/lox/test_parser.rb

@@ -90,6 +90,10 @@ class TestParser < Lox::Test
     assert_parsed <<~AST.chomp, :statement, "for(var i=0; i<3; i=i+1) print i;"
       (block (var i 0.0) (while (< (var i) 3.0) (block (print (var i)) (assign i (+ (var i) 1.0)))))
     AST
+
+    assert_parsed <<~AST.chomp, :statement, "for(var i=0; ; i=i+1) print i;"
+      (block (var i 0.0) (while true (block (print (var i)) (assign i (+ (var i) 1.0)))))
+    AST
   end
 
   private