cond
COND clauses (library procedure)
command or operation. The input is a list of lists (clauses); each
clause is a list whose first element is either an expression whose
value is TRUE or FALSE, or the word ELSE, and whose butfirst is a Logo
expression or instruction. COND examines the clauses in order. If a
clause begins with the word ELSE (upper or lower case), then the
butfirst of that clause is evaluated and CASE outputs its value, if
any. Otherwise, the first element of the clause is evaluated; the
resulting value must be TRUE or FALSE. If it's TRUE, then the
butfirst of that clause is evaluated and COND outputs its value, if
any. If the value is FALSE, then COND goes on to the next clause. If
no clause is satisfied, COND does nothing. Example:
to evens :numbers ; select even numbers from a list
op cond [ [[emptyp :numbers] []]
[[evenp first :numbers] ; assuming EVENP is defined
fput first :numbers evens butfirst :numbers]
[else evens butfirst :numbers] ]
end