Item2356: QUERY and IF are a little un-intuitive for simple queries

I was thinking about optimising parsed queries (basically for true&false to be nop's) and thought I'd examine what the code thinks is truthieness..

I'm not sure its 'right' in the head

sub test_true {
    my $this = shift;
    
    #nope, parse failure (empty Expression) :/
    #$this->simpleTest( test => "0", then => 1, else => 0 );#A
    
    $this->simpleTest( test => "1", then => 1, else => 0 );#B
    $this->simpleTest( test => "9", then => 1, else => 0 );#C
    #surprisingly..
    $this->simpleTest( test => "-1", then => 1, else => 0 );#D
    $this->simpleTest( test => "-0", then => 1, else => 0 );#E

    $this->simpleTest( test => "0.0", then => 1, else => 0 );#F
    
    ##and again as strings..
    $this->simpleTest( test => "'1'", then => 1, else => 0 );#G
    $this->simpleTest( test => "'9'", then => 1, else => 0 );#H
    #surprisingly..
    $this->simpleTest( test => "'-1'", then => 1, else => 0 );#I
    $this->simpleTest( test => "'-0'", then => 1, else => 0 );#J

    $this->simpleTest( test => "'0.0'", then => 1, else => 0 );#K
}

sub test_false {
    my $this = shift;
    $this->simpleTest( test => "not 1", then => 0, else => 1 );#L
    $this->simpleTest( test => "1 = 2", then => 0, else => 1 );#M

    ##and again as strings..
    $this->simpleTest( test => "'0'", then => 0, else => 1 );#N

}

commited to trunk's Fn_IF.pm

it also worries me a little that the number zero is internally the representation for false, but that when parsing user input, the number zero is considered undefined.

-- SvenDowideit - 14 Nov 2009

You don't say what result you expect in each case. However the new tests show up a couple of parser problems, that I've fixed. Better?

-- CrawfordCurrie - 15 Nov 2009

some notes:

The number 0, the strings ’0’ and ’’, the empty list "()", and "undef" are all false in a boolean context. All other values are true. Negation of a true value by "!" or "not" returns a special false value. When evaluated as a string it is treated as ’’, but as a number, it is treated as 0.

=man perlsyn=

True or False? A Quick Reference Guide including lots of truth tables and other handy charts

use 0 but true when useful (which means exactly what it says)

-- WillNorris - 16 Nov 2009

lets call it much better

-- SvenDowideit - 02 Jul 2010