Conditional structures: Difference between revisions

===[http://docs.racket-lang.org/reference/when_unless.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._when%29%29 when/unless]===

One-sided conditional expressions use "when" and "unless". These are more convenient for side-effects since they have an implicit "begin" around their body, and you can also include new definitions

<lang Racket>

(when (< x 10)

(define y (* x 10))

(printf "small\n"))

</lang>

===[http://docs.racket-lang.org/reference/if.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._cond%29%29 cond]===

Used for multiple conditions:

<lang Racket>

(printf "x is ~a\n"

(cond [(< x 1) "tiny"]

[(< x 10) "small"]

[(< x 100) "medium"]

[(< x 10000) "big"]

[(< x 100000000) "huge"]

[else "gigantic"]))

</lang>

===[http://docs.racket-lang.org/reference/case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29 case]===

Similar to a "switch" statement in other languages

<lang Racket>

(case x

[(1) "one"]

[(2) "two"]

[(3) "three"]

[(4) "four"]

[(6 8) "even"]

[(5 7 9) "odd"]

[else "something else"])

</lang>

===etc===

Racket has macros, which means that you can define whatever new conditional you think is useful...