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Feature #3845

Updated by matz (Yukihiro Matsumoto) over 12 years ago

=begin 
  
  Hi, 
 
  I'd propose "in" infix operator. 
 
  (<arg> in <args>) yields true when <arg> is included in <arg>. 
  Otherwise it yields false. 
 
 
    p "found"       if 1 in 1, 2, 3    #=> found 
    p "not found" if 0 in 1, 2, 3    #=> not found 
 
 
  "in" operator is clearer to the reader than Array#include?: 
 
    p "found"       if [1, 2, 3].include?(1) 
    p "not found" if [1, 2, 3].include?(0) 
 
 
  This proposal is similar to Object#in? proposed in [ruby-core:23543]. 
  But there are two differences: 
 
    - "in" operator does not pollute name space of Object class 
 
    - each candidate of "in" is evaluated lazily; for example, 
 
        1 in 1, 2, foo() 
 
      does not call the method "foo" because 1 is found before that. 
 
 
  Note that this proposal ensures the syntax compatibility, since 
  "in" is already a keyword for "for" statement.    But "for" statement 
  is rarely used.    This proposal utilizes the rarely-used keyword. 
 
 
  I wrote an experimental patch.    It implements the operator as a 
  syntactic sugar to "case" statement: 
 
    <arg> in <args> 
      =>    (case <arg>; when <args>; true; else false; end) 
 
  The patch causes no parser conflict. 
 
 
  One more thing.    The following expression is rejected: 
 
    foo(x in 1, 2, 3) 
 
  This is because it is ambiguous; this expression can be interpreted 
  as three ways: 
 
    foo((x in 1), 2, 3) 
    foo((x in 1, 2), 3) 
    foo((x in 1, 2, 3)) 
 
  You need write parentheses explicitly. 
 
 
  What do you think? 
 
 
  diff --git a/parse.y b/parse.y 
  index e085088..64318bd 100644 
  --- a/parse.y 
  +++ b/parse.y 
  @@ -745,6 +745,7 @@ static void token_info_pop(struct parser_params*, const char *token); 
   %nonassoc    modifier_if modifier_unless modifier_while modifier_until 
   %left    keyword_or keyword_and 
   %right keyword_not 
  +%nonassoc keyword_in 
   %nonassoc keyword_defined 
   %right '=' tOP_ASGN 
   %left modifier_rescue 
  @@ -1258,6 +1259,14 @@ expr 		 : command_call 
  			 $$ = dispatch2(unary, ripper_id2sym('!'), $2); 
  		     %*/ 
  		     } 
  + 		 | expr keyword_in args 
  + 		     { 
  + 		     /*%%%*/ 
  + 			 $$ = NEW_CASE($1, NEW_WHEN($3, NEW_TRUE(), NEW_FALSE())); 
  + 		     /*% 
  + 			 $$ = dispatch2(in, $1, $3); 
  + 		     %*/ 
  + 		     } 
  		 | arg 
  		 ; 
  
  diff --git a/test/ripper/test_parser_events.rb b/test/ripper/test_parser_events.rb 
  index 5d76941..6005457 100644 
  --- a/test/ripper/test_parser_events.rb 
  +++ b/test/ripper/test_parser_events.rb 
  @@ -1107,4 +1107,8 @@ class TestRipper::ParserEvents < Test::Unit::TestCase 
       parse('/', :compile_error) {|msg| compile_error = msg} 
       assert_equal("unterminated regexp meets end of file", compile_error) 
     end 
  + 
  +    def test_in 
  +      assert_equal("[in(1,[1,2,3])]", parse('1 in 1, 2, 3')) 
  +    end 
   end if ripper_test 
 
  --  
  Yusuke Endoh <mame@tsg.ne.jp> 
 
 =end 
 

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