Boolean operation: (A & B) vs (A * B)

[Anonymous Monk]

Hi

In Boolean function evaluations using Perl, what is the difference between these two expressions:

#1 Y = (A & B)
#2 Y = (A * B)

I cannot seem to find documentation on the #2 form of expression, even though I have seen #2 in Boolean expressions used in Perl. For example, this thread has #2 style: parser for evaluating arbitrarily complex boolean function in a string

Bill Murphy

[LanX]

In mathematics (i.e. boolean algebra) it is common to denote * for and and + for or IFF the alphabet is restricted to boolean values 0 and 1.

NOTE: 1 + 1 is mapped to 1 there.

This works in Perl somehow. (1+1 =2 is still true)

But don't ! It's not recommended ... rather a workaround in languages without boolean operators.²

Just sketch the truth table to see how it works.

Better use && and || instead.

> Y = (A & B)

that's definitely wrong, because & is for a bitwise and not a logical.

UPDATE

to elaborate more: the standard false value in Perl is not 0 but empty string '' . While the latter will be evaluated to 0 in arithmetic operations it might cause a confusion.

DB<7> print !!0

DB<8> print  !!1
   1

footnotes

²) and only for simple cases, b/c you risk a number overflow when multiplying true values.

> perl -E "say ((1+1) * (1+1) * (1+1));"
8

[GotToBTru]

The multiplication operator and the bitwise AND are obviously not the same, but if the only values for A and B are 0 or 1, A * B will produce the same truth table as A && B.

Update: replaced & with && per LanX.

[hippo]

A * B is a numerical multiplication. If the (perl) values of A and B can only be 1 and 0 then this is equivalent to a Boolean AND.

A & B is a bitwise AND. Again, if 1 and 0 are the only values this is also equivalent to a Boolean AND.

Whether or not these expressions are entirely equivalent depends on the restrictions of the values to the binary set {0, 1}.

[LanX]

> If the (perl) values of A and B can only be 1 and 0 then this is equivalent to a Boolean AND.

well it's a bit more complicated... 1+1 = 2, see my post Re: Boolean operation: (A & B) vs (A * B)

Update

as pointed out neither the OP nor hippo used +, I saw the wider scope ...

[kennethk]

All Perl operators are documented in perlop. Relevant for this conversation:
• * -- Multiplicative Operators
• & -- Bitwise And
• && -- C style Logical And
• and -- Logical And

Also, to get parser for evaluating arbitrarily complex boolean function in a string, write [id://399322] as documented in Markup in the Monastery.

[u65]

To ease analysis that node link is 399322.