CODEWITHSUNDEEP
lispclojureboolean
Onorio Catenacci
Onorio Catenacci

Reputation: 15303

The Clojure (or Lisp) Equivalent of a Compound Boolean Test

In C++ I'd write something like this:

if (a == something && b == anotherthing)
{
   foo();
}

Am I correct in thinking the Clojure equivalent is something like this:

(if (= a something)
    (if (= b anotherthing)
        (foo)))

Or is there another way to perform a logical "and" that I've missed? As I said the latter form seems to work correctly--I was just wondering if there's some simpler way to perform the logical and. And searching for "boolean" "logical" and "and" on the Clojure Google Group turned up too many results to be much use.

Upvotes: 21

Views: 4472

Answers (4)

Ralph
Ralph

Reputation: 32294

It's really cool! (and x y) is a macro -- you can check the source code at clojure.org -- that expands to (if x y false) equivalent to:

if (x) {
  if (y) {
    ...
  }
} else {
  false
}

(or x y) is similar but reversed.

Upvotes: 2

mikera
mikera

Reputation: 106361

In Clojure I would normally use something like:

(if 
  (and (= a something) (= b anotherthing))
  (foo))

It is clearly possible to be more concise (e.g. Doug's answer) but I think this approach is more natural for people to read - especially if future readers of the code have a C++ or Java background!

Upvotes: 8

David Lichteblau
David Lichteblau

Reputation: 3561

In Common Lisp, the following is also a common idiom:

(when (and (= a something) (= b another))
  (foo))

Compare this to Doug Currie's answer using (and ... (foo)). The semantics are the same, but depending on the return type of (foo), most Common Lisp programmers would prefer one over the other:

  • Use (and ... (foo)) in cases where (foo) returns a boolean.

  • Use (when (and ...) (foo)) in cases where (foo) returns an arbitrary result.

An exception that proves the rule is code where the programmer knows both idioms, but intentionally writes (and ... (foo)) anyway. :-)

Upvotes: 17

Doug Currie
Doug Currie

Reputation: 41180

In Common Lisp and Scheme

(and (= a something) (= b another) (foo))

Upvotes: 35

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