cond
Categories: Keywords procedures
, Conditional procedures
;;; (cond [guard0 exp0a exp0b ...] [guard1 exp1a exp1b ...] ... [else alt0 alt1 ... altn])
;;; guard0 : expression?
;;; exp0a : expression?
;;; exp0b : expression?
;;; ...
;;; guard 1 : expression?
;;; exp1a : expression?
;;; ...
;;; alt0 : expression?
;;; alt1 : expression?
;;; ...
;;; altn : expression
;;; Evaluate each guard in turn until one holds (is not false). Then evaluate
;;; each of the corresponding expressions. Return the value of the last
;;; corresponding expression. If none of the guards holds, evaluate each
;;; of `alt0` through `altn`, returning the value of `altn`.
We traditionally format cond expressions as follows.
(cond
[guard0
exp0a
...
exp0x]
[guard1
expt1a
...
exp1y]
...
[else
alt0
...
altn])
That is,
cond block is on a separate line from the cond.cond block.Most of the procedures we learn early on have no “side effects” (that is, they do not affect the state of the system). Hence, it is often pointless to have more than one expression in each cond block. However, once we learn procedures that can generate output, modify a structure, or otherwise affect the state of the system, it becomes useful to have multiple expressions in each block.
Forthcoming
Forthcoming