HPlogo System Debug Reference Manual > Chapter 5 System Debug Command Specifications Fx-LOG

IF

MPE documents

Complete PDF
Table of Contents
Index

E0201 Edition 4 ♥
E0300 Edition 3
E0692 Edition 3

If condition evaluates to TRUE, then execute all commands in cmdlist, else execute all commands in cmdlist2.

Syntax


   IF condition THEN command

   IF condition THEN { cmdlist }

   IF condition THEN command1 ELSE command2

   IF condition THEN { cmdlist } ELSE command2

   IF condition THEN command1 ELSE { cmdlist2 }

   IF condition THEN { cmdlist } ELSE { cmdlist2 }

Parameters

condition

A logical expression to be evaluated.

command cmdlist

A single command (or command list) that is executed if condition evaluates to TRUE.

command2 cmdlist2

A single command (or command list) that is executed if condition evaluates to FALSE.

Note that in nested IF-THEN-ELSE clauses, the first ELSE clause always matches the first IF clause. This is different from the conventions of most compilers, and it may not be intuitive. Explicit use of {cmdlists} is recommended in these nested cases.

Examples


   %cmdebug > if [q-3]>[db+4] then c
If the contents of Q-3 are greater than the contents of DB+4, then continue. 

   $nmdebug > if (length>20) and (pcsf=a) then {wl "GOT IT"; c}
If the value of the variable length is greater than 20, and the contents of the predefined variable pcsf equals $a, then execute the following from the command list: print the string "GOT IT", then continue. 

   $nmdat > if 1 then {if 0 then wl "wee" else wl "willy"} else wl "wonka"
   willy
This example shows a nested IF-THEN-ELSE clause within a cmdlist clause.

Limitations, Restrictions

The interpreter does not parse or analyze the contents of the clauses prior to their execution. Based on the value of the condition, the THEN or ELSE clause is be executed, and the other clause disregarded.

This implies that the clauses may be syntactically illegal, but the errors are not discovered until they are executed.

Note that in the following examples, entire clauses are bogus, but not detected: 

   $nmdebug > if TRUE then wl "good" else XXXXXXXXXXXXXXXXXX
   good

   $nmdebug > if FALSE then XXXXXXXXXXXXXXXX else wl "good"
   good



HIST[ORY]

IGNORE