Control flow¶

BPP+ labels can be used anywhere BASIC v2 accepts line numbers for control flow. During transpilation, labels are replaced with their corresponding line numbers.

Unconditional transfer¶

goto <label>            rem Absolute jump
gosub <label>           rem Subroutine call with return
return                  rem Return from subroutine

Conditional transfer¶

if <condition> then goto <label>    rem Explicit GOTO
if <condition> then <label>         rem Implicit GOTO (just the label)
if <condition> then <statement>     rem Conditional execution (standard BASIC)
if <condition> then gosub <label>   rem Conditional subroutine call

Implicit vs explicit GOTO¶

In BPP+ source, if <condition> then <label> transpiles to if <condition> then <line_number>. In BASIC v2, when the THEN clause contains only a number, BASIC interprets it as an implicit GOTO to that line number.

Transpilation example¶

rem Source (.bpp)

if x=1 then done                rem Implicit GOTO
if x=1 then goto done           rem Explicit GOTO

done:
    print "finished"

rem Output (.bas)

1 ifx=1then3                    rem Implicit form
2 ifx=1thengoto3                rem Explicit form
3 print"finished"

Performance trade-off¶

The explicit form if <condition> then goto <label> is faster to execute, though it uses one extra token byte (the GOTO keyword). The implicit form if <condition> then <label> is more memory-efficient but slightly slower. Choose based on whether speed or memory is more critical for your application.

Computed transfer¶

on <expression> goto <label1>, <label2>, ...
on <expression> gosub <label1>, <label2>, ...

Expression evaluates to 1-based index. Out-of-range values fall through to next statement.

Scope-qualified labels in ON statements¶

ON statements support fully-qualified label paths:

menu: {
    opt1:
        print "option 1":return

    opt2:
        print "option 2":return

    opt3:
        print "option 3":return
}

main:
    input "choice (1-3)"; choice
    on choice gosub menu.opt1, menu.opt2, menu.opt3
    end

This transpiles to line numbers like any other label reference:

1 input"choice (1-3)";choice
2 onchoicegosub3,4,5
3 end
4 print"option 1":return
5 print"option 2":return
6 print"option 3":return

Performance considerations¶

Branching overhead¶

All branching operations (GOTO, GOSUB, IF...THEN with line numbers) require the BASIC interpreter to search through program lines to find the target:

Forward jumps search from the current position.
Backward jumps search from the beginning of the program, making them progressively slower as program size increases.

Loop performance¶

FOR...NEXT loops are faster than backward GOTO loops because NEXT stores the exact return address on the stack instead of performing a line search. When possible, prefer FOR...NEXT over GOTO-based loops.