Thomas Lake  wrote:   
   > On Wednesday, April 11, 2018 at 6:33:17 AM UTC-4, Shaun Bebbington wrote:   
   >> Hi,   
   >>   
   >> I found something odd today in the powerful CBM BASIC v2.0.   
   >>   
   >> Having worked with Sinclair BASIC quite a lot recently, I use GOTO X where X   
    is a valid line number (i.e., LET X = 100). But I know that's not possible   
   with Microsoft BASIC. Of course there is the ON X GO TO 100,200 ...   
   >>   
   >> So I thought "I know, I'll try and use a function, could CBM BASIC use this   
   as a look up table". The following, I expected to go to the value in the   
   function A() which returns 10, but...   
   >>   
   >> 0 DEF FN A(X) = 10   
   >> 1 PRINT FN A(0)   
   >> 2 GO TO FN A(0)   
   >> 3 PRINT "END GRACEFULLY"   
   >> 4 END   
   >> 10 PRINT "STOP"   
   >> 11 STOP   
   >>   
   >> Try it for yourself. What's going on here?   
   >>   
   >> Thanks in advance.   
   >>   
   >> Shaun.   
   >   
   > You SHOULD get a syntax error. Commodore (Microsoft) BASIC is supposed to   
   only allow numeric constants, not variables after GOTO and GOSUB. What do you   
   actually see happening?   
      
   Not exactly how BASIC V2 parses it. GOTO parses all digits (ignoring   
   blanks everywhere in between) and stops a the first non-digit character.   
   In this case GOTO stops right before the FN token. So, the parsed line   
   number is empty. The fallback (evaluation) for an empty line number   
   argument is 0. Therefore GOTO jumps to line 0 and starts over.   
      
   As others suggested already, one should use ON  GOTO ... to   
   use a calculated form of GOTO, or using a patched GOTO, or using the   
   display containing a prepared GOTO statement with keyboard   
   buffer ... could go like this   
      
   100 PRINT "{CLRSCR}{DOWN}{DOWN}GOTO "500+500"{HOME}";   
   110 POKE631,13: REM RETURN INTO KEYBOARD BUFFER   
   120 POKE198.1: REM KEYBOARD BUFFER LENGTH   
   130 END: REM HERE   
   1000 PRINT "WE REACHED LINE 1000"   
      
      
   Johann   
      
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