REBOL 3 Functions: all

Description

The all function is the most common way to test multiple conditions, such as in the line:

if all [num > 1  num < 1000] [do something]

It works by evaluating each expression in a block until one of the expressions returns none! or false, in which case a none! is returned. Otherwise, the value of the last expression will be returned.

print all [1 none]
none

print all [none 1]
none

print all [1 2]
2

print all [10 > 1 "yes"]
yes

print all [1 > 10 "yes"]
none

time: 10:30
if all [time > 10:00 time < 11:00] [print "time is now"]
time is now

No other expressions are evaluated beyond the point where a value fails:

a: 0
all [none a: 2]
print a
0

a: 0
all [1 a: 2]
print a
2

day: 10
time: 9:45
ready: all [day > 5  time < 10:00  time: 12:00]
print time
12:00

The any function is a companion of all to test for the opposite condition, where any one of the values will result in a true result.