if booleanexpr then statement

if booleanexpr then
statement(s)
end if

if booleanexpr then
statement(s)
else
statement(s)
end if

A single line IF evaluates booleanexpr, when true the statement(s) following the then is executed, otherwise execution continues on the next line. There are also two forms of a multi-line if statement, one with a true block and one with a true and a false block of code to execute.

print "Guess my letter - press a key"
# wait for the user to press a key
do
  a = key
  pause .01
until a <> 0
#
if chr(a) = "Z" then
   print "Yippie, you pressed the Z key!!!"
else
   print "darn, you pressed something else."
end if
#
end

0.9.4g