Re: LOGO-L> QUESTION ON CONDITIONAL OUTPUTS

[Chuck Shavit <CShavit@MagicSquare.com>]

George Mills writes:

> A young programmer should understand the value of
> good error checking.
>
>>         ADDLISTS doesn't like [3 4 A 6] as input
>
> Again these arguments seem trivial either way with the
> ADDLISTS example. But when programs get large and complex
> with one thing built on top of another good skills in
> making the code readable and error checking
> begin to pay back.
>
> This could just as easily say:
>
> ADDLISTS doesn't like the non numeric element 3 in the input [3 4 A 6]

I agree to everything George writes in this post.  Good error detection and
reporting is as important in a library procedure as it is in the guts of
the interpreter.

I'd like to add two points:

  1. Some of the rigorous error reporting can be relexed if a readable
     traceback is provided.  Something like
       ADD cannot add a non numeric value.  It had inputs A and 3.
       It was called from ADDLISTS [A 6] [9 2]
       Which was called from ADDLISTS [4 A 6] [1 9 2]
       Which was called from ADDLISTS [3 4 A 6] [8 1 9 2]
       Which was called from the command line.

  2. I personally am not crazy about the "humanized" style of Logo messages,  
     like the two examples above.  A computer is just a machine, not a cute
     being that "likes" some things and "cannot do" other things, IMO.

Chuck Shavit
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