Command or operation where:
condition evaluates to TRUE, then IF runs
condition evalutes to FALSE, then IF does nothing.
If given a
false.instructionlist input, IF acts like IFELSE.
It is an error if
condition does not evaluate to either TRUE or FALSE.
For compatibility with earlier versions of Logo, if an IF instruction is not enclosed in parentheses, but the first thing on the instruction line after the second input expression is a literal list (i.e., a list in square brackets), the IF is treated as if it were IFELSE, but a warning message is given. If this aberrant IF appears in a procedure body, the warning is given only the first time the procedure is invoked in each Logo session.
; single instruction list IF 1=1 [PRINT [Yes it is true]]Yes it is true
; two instruction lists TO MAX :a :b OUTPUT (IF :a > :b [:a] [:b]) END SHOW MAX 1 22