Posted: 01:36pm
14 Jun 2025
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robert.rozee
Guru
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i don't know if this has been brought up before, but... while adding a pause/resume ability to a program, i found an interesting anomaly in the way the MX170 version of mmbasic handles DO...LOOP within single-line if statements. here is a quick works/fails example i put together: Print "expanded - works correctly"
n=1
Do
i=1
Print ">";
If n>0 Then
Do : Print n,: i=i+1: n=n+1: Loop Until (i>8) Or (n>52)
EndIf
Print
Loop Until n>52
Print
Print "compact - Do's get mixed up"
n=1
Do
i=1
Print ">";
If n>0 Then Do : Print n,: i=i+1: n=n+1: Loop Until (i>8) Or (n>52)
Print
Loop Until n>52
End and here are the results of running the example: > Micromite MKII MMBasic Ver 5.05.05
Copyright 2011-2022 Geoff Graham
> RUN
expanded - works correctly
> 1 2 3 4 5 6 7 8
> 9 10 11 12 13 14 15 16
> 17 18 19 20 21 22 23 24
> 25 26 27 28 29 30 31 32
> 33 34 35 36 37 38 39 40
> 41 42 43 44 45 46 47 48
> 49 50 51 52
compact - Do's get mixed up
> 1 > 2 > 3 > 4 > 5 > 6 > 7 > 8 > 9 > 10
> 11 > 12 > 13 > 14 > 15 > 16 > 17 > 18 > 19 > 20
> 21 > 22 > 23 > 24 > 25 > 26 > 27 > 28 > 29 > 30
> 31 > 32 > 33 > 34 > 35 > 36 > 37 > 38 > 39 > 40
> 41 > 42 > 43 > 44 > 45 > 46 > 47 > 48 > 49 > 50
> 51 > 52
[20] Loop Until n>52
Error : LOOP without a matching DO
> essentially, the interpreter is picking up the wrong DO when the IF...THEN DO...LOOP is all on a single line. i don't really consider this a bug as such, but perhaps the manual should be appended to say that IF...THEN DO...LOOP all on one line should be avoided! btw: the code where i encountered this problem was along the lines of: Do
key = Asc(Inkey$)
If key=Asc("p") Then Do :Loop Until Inkey$<>""
Print Timer
Loop cheers, rob :-)
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true, the code presented here is deliberately crafted just to isolate the behavior of interest; when identifying such 'corner cases' you often have to do unexpected/odd things that the average user should NOT normally be doing anyway. but it IS still important to know about these corner cases, so as to document them so others don't accidentally get caught out.