What is the use of non short-circuiting boolean operators in Erlang?
Question
I am learning Erlang from the LearnYouSomeErlang web-book. One thing that struck me while learning was the non short-circuiting boolean conjunction and disjunction operators viz; and
and or
. What are the use cases for these operators? Why would you want to use them instead of andalso
and orelse
?
Solution
It used to be (until R13A) that andalso
and orelse
weren't tail recursive. See http://www.erlang.org/eeps/eep-0017.html for details. I don't think there is a good reason to use and
/or
in new programs.
OTHER TIPS
I see them as doing different things and use them as such:
and
/or
as logical operators where I want to compare the logical values. As they are strict I automatically get type-checking and I KNOW exactly what has been called.andalso
/orelse
for control, much like&&
and||
in C.
Seeing errors are defined in erlang I feel it is good to know what has been executed and how it went.
The and/or operators are simply much older. The andalso/orelse operators are later additions. A use case for and/or today could be when you just want to perform some simple boolean operations and horizontal space is more important than possibly saving a couple of machine cycles. For example:
X = Y and (A or B),
rather than
X = Y andalso (A orelse B),
is a bit easier on the eyes.
For reasons of backwards compatibility, it wasn't possible to just change the behaviour of the original and/or to become short-circuiting, so new keywords were needed. The names andalso/orelse come from Standard ML.