HELP AND J. L. Cunningham Jul 1982
Updated: Adrian Howard Mar 1992
The infix operator -and- is used to form a "conjunction" of two
expressions. For example:
<P> and <Q>
This expression will return the value of the expression <Q> if both <P>
and <Q> evaluate to non-false values. If either <P> or <Q> is -false-,
then -false- is returned.
The expression <P> is evaluated first. If <P> is -false- then the whole
expression evaluates to -false- immediately and <Q> is not evaluated. If
<P> is not -false- then <Q> is evaluated. If <Q> is not -false- as well,
then -true- is return. This is known as "lazy" evaluation --- only the
expressions that need to be evaluated are evaluated.
Normally -and- will be used with *BOOLEAN expressions, when it can be
treated like a logical "and" operation. Some programming languages
require the value of expressions used in conditions, e.g. after the
syntax word *IF, to be boolean, but POP does not --- it treats any value
which isn't -false- as true.
There is also a bitwise logical 'and' operator (&&) on integers treated
as a sequences of "bits", see REF *NUMBERS/Bitwise for details.
Also see:
HELP *OR --- Forming disjunctions in POP-11
HELP *BOOLEAN --- Boolean expressions and values
HELP *CONDITIONALS --- Summary of POP-11 conditional statements
REF *RECORDS/Booleans --- Full information on "booleans"
--- C.all/help/and
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