Re: [WWdevel] Predefined constants like NONE and DNE

[John J. <jj...@as...>]

I would like to see having this short list of strings always recognized 
by webwork.  I don't see any harm in it, and it will make some problems 
function better.

John


Davide P.Cervone wrote:

> Folks:
>
> When I wrote the Parser code, one of the things I was after was 
> consistency in terms of error messages.  Since the same parser was 
> being used for ALL types of answers, it would know about the other 
> types of objects no matter what type of answer you were looking for.  
> For example, if you are checking for a numeric answer, the Parser 
> still will give appropriate error messages even when the student types 
> an interval: it will say something to the effect that you typed an 
> interval but that it expected a number.  Since you have the ability to 
> change the Context, however, that somewhat undermines this, since you 
> can remove its knowledge of some types of objects (e.g., the Numeric 
> class does not know about points).
>
> When I developed the Legacy module for the Parser, which makes num_cmp 
> and fun_cmp use the Parser answer checkers, I implemented contexts 
> that mirrored the traditional num_cmp and fun_cmp environments as 
> closely as I could.  This is the right thing to do for backward 
> compatibility, but I'm not sure it is the best idea for the future.  
> For example, all the default Parser contexts include definitions for 
> NONE, INF, INFINITY, -INF, -INFINITY, and DNE, as common strings that 
> might be used in other parts of the problem, so the Parser should 
> recognize these and respond appropriately when the student enters them 
> when some other type of answer is expected (usually they are marked 
> incorrect silently).  I took these out of the num_cmp and fun_cmp 
> contexts, however, so if a student types NONE in an answer blank for 
> num_cmp, he or she will get an error message instead (but it will at 
> least be "'NONE' has no meaning in this context" rather than a message 
> about an undefined variable 'N').
>
> I think that in the long run, NONE, DNE, and the infinities should all 
> be defined all the time.  Do you think these should be added back into 
> the Parser-based versions of num_cmp and fun_cmp?
>
> Davide
>
>
>
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