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Forum Index : Microcontroller and PC projects : interesting DO...LOOP anomaly in mmbasic (MX170, 5.05.05)
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| robert.rozee Guru  Joined: 31/12/2012 Location: New ZealandPosts: 2428 |
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 Loop Until n>52 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) 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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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7820 |
I think I've seen that come up before. The error checking on the MX170 version can be a bit lax in some places, probably due to the available memory - you can't trap everything. As it's really an embedded control version this sort of error is only really an item during development. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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vegipete Guru Joined: 29/01/2013 Location: CanadaPosts: 1127 |
What happens if you put a ":" after "THEN" and finish the single line with "ENDIF"? Visit Vegipete's *Mite Library for cool programs. |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2579 |
@vegipete is right. As far as I can tell all versions of MMBasic need both "THEN :" and "ENDIF" in multi statement lines. Without them the implied EndIf could belong anywhere, not just the end of the line. If key=Asc("p") Then : Do :Loop Until Inkey$<>"" : ENDIF |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6266 |
THEN followed by DO has a problem. Inserting a ":" will fix the problem without any need for the ENDIF In all other cases the ":" is not required as per the manual VK7JH MMedit |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2579 |
Yes, tried on MM2 v5 05.05 and PicoMite v6.00.02. n=1:do:i=1:?">",:If n>0 Then : Do : ? n,: i=i+1: n=n+1: Loop Until (i>8) Or (n>52):?:Loop Until n>52 |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2428 |
Jim, Phil, Pete: the colon does fix the example i gave, but not the one generated by this code: Do If Inkey$="p" Then:Do :Print ".";:Loop Until Inkey$<>"" Print "#"; Loop > Micromite MKII MMBasic Ver 5.05.05 Copyright 2011-2022 Geoff Graham > RUN [2] If Inkey$="p" Then:Do :Print ".";:Loop Until Inkey$<>"" Error : No matching ENDIF > and with the colon removed again, we are back to: > > list Do If Inkey$="p" Then Do :Print ".";:Loop Until Inkey$<>"" Print "#"; Loop > > RUN # [4] Loop Error : LOOP without a matching DO > i really do think a "do not do this" note in the manual is the best solution! cheers, rob :-) Edited 2025-06-16 00:01 by robert.rozee |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2428 |
but this DOES work, even though it shouldn't: Do If Inkey$="p" Then:Do :Print ".";:Loop Until Inkey$<>"":EndIf Print "#"; Loop cheers, rob :-) |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7820 |
It's always better to make your programs readable though. Complex single-line statements get very confusing. Anyone would think that you had to pay for CRLF and pretty-printing. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2428 |
 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.cheers, rob :-) |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2579 |
After encountering similar errors I had found the EndIf fixed it and assumed it to always be necessary in multi-statement IF lines. Until Jim showed it isn't always the case. It works because with the EndIf included it becomes a regular multi-line IF with the ":" replacing CRLFs |
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