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The concept of 'and' in perl programming and logic, as well as the concept of quantification. It covers truth tables, parallel assignment, and parameterized predicates. It also includes exercises and examples for understanding these concepts.
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sub TRUE { 1 } sub FALSE { undef } if ($_[0]) { return "true "; } else { return "false"; } sub BoolText { } print BoolText($b1). " "
. BoolText($b2). " " . BoolText(! ($b1 && $b2)) . "\n"; foreach my $b2 (&FALSE, &TRUE) { } foreach my $b1 ( &FALSE, &TRUE ) { } My version Docsity.com
@a = (1,2,3); print "first item is $a[0]\n"; print "second item is $a[1]\n"; print "third item is $a[2]\n"; An array is a list of items. Note that the array is @a, but an element is of the form $a[$i]. In other words, something that starts with @ is an array, while something that starts with $ is a scalar , even if it is an array element! Arrays in Perl Docsity.com
Perl has a unique feature called parallel assignment. ($a, $b, $c)=(1,42, "hello"); One can write to set $a to 1, $b to 42, and $c to "hello". ($a,$b,@c)=(22,"hi","ho","there"); One can write to set $a to 22, $b to "hi", and @c to ("ho", "there") The last array consumes the remaining elements. Parallel assignment Docsity.com
my ($cat, $dog) = @_; print "my cat's name is $cat\n"; print "my dog's name is $dog\n"; sub identify { } Typical use of parallel assignment: writing subroutines &identify("Fred", "George"); If we then write my cat's name is Fred my dog's name is George then in the subroutine after the assignment, $cat eq "Fred" and $dog eq "George", and this will print Writing subroutines Docsity.com
&&, and: in Perl : in logic We now have two concepts of "and" We use && to denote something to do , i.e., A && B is a command that computes a value (true or false). We use to denote "a statement about the world". A B is not a command, but rather, a description of state. What is the difference? Why are logic and programming symbols different? Docsity.com
So far, logic has been a matter of manipulating symbols. map reality into symbols, and map results to reality. In fact, logic is only useful if one can One key to making logic useful: "quantification". Making logic useful Docsity.com
Every variable in a parameterized predicate has a domain : a set of reasonable values. x is in the domain of machines in our building. P(x)="machine x is working." x is in the domain of numbers. Q(x)="x>10" A "parameterized predicate" is a statement of the form P(x) where x is a variable. Parameterized predicates Docsity.com
