Re: Ann: SWI-Prolog 7.1.0

Hi Jan

Thanks for the explanation, it seems clear for me now

On Saturday 23 November 2013 17:39:14 Jan Wielemaker wrote:
> There are several typical cases. One concerns that you map data from a
> language that can uniquely identify lists from symbols, such as JSON.
> Such languages cannot be mapped naturally to Prolog because it is
> unclear whether [] is some kind of identifier or an empty list. Another
> are expressions such as consult([]), which may mean to consult the file
> '[].pl' or consult nothing. Same for format("", []) with double quotes
> set to 'codes': does this write '' (nothing) or '[]'?
> 
> In practical programming, you have cases where you have a list of
> `tokens' (atoms) and you want to explode some tokens or other special
> symbols into a sequence. The clean way is to use DCGs or difference list
> to create a nice and flat holding the expansion. In some cases however,
> it is way simpler if you can just explode the objects into lists, so you
> get [ 'The', [quick, brown, fox], jumps, over, the, [lazy dog] ].
> 
> This is all fine, until '[]' may appear as a token in the list.  In that
> case, flatten/2 just removes it.  Due to the ambiguity of the empty list,
> creating a multi list and call flatten/2 is considered bad programming.
> Without this ambiguity, using multi lists is safe and can be a handy
> solution, in particular for the not-so-experienced Prolog programmer.
> 
> 	Cheers --- Jan

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