Print Page - implicit indexing on empty string

Title: implicit indexing on empty string
Post by: jef on October 13, 2014, 12:51:54 PM

I'm surprised that implicit indexing doesn't raise an error

on an empty string (when called with 0 or -1), while it

does on an empty list:

> ("" 0)

""

> ("" -1)

""

With another index, we get an error as expected:

> ("" 1)

ERR: invalid string index

If we compare to implicit indexing on an empty list, we always

get an error:

> ('() 0)

ERR: invalid list index

>('() -1)

ERR: invalid list index

Any explanation for this?

(btw, thanks again Lutz, newLISP is a real pleasure to use)

Title: Re: implicit indexing on empty string
Post by: Lutz on October 14, 2014, 12:38:01 AM

An empty string is not like an empy list:

Code Select Expand

> (push "" "")
""
> (push '() '())
(())
> (atom? "")
true
> (atom? '())
nil
>

an empty list is still a container. The only alternative would be to return nil for ('() 0) - not the symbol nil but the boolaean value nil. This was done in early versions of newLISP. But while programming, it seemed to make more sense to throw an error message.

But still today:

Code Select Expand

> (pop '())
nil

... practical for processing lists with pop.

There are other inconsistencies like this in newLISP: the function dup on lists and strings, nil as a boolean value and a symbol, treatment of () and nil - to name a few. When these conflicts occur in newLISP, they are normally decided by the occurrance of real world usage patterns and their practicality rather then trying to be consistent.

Title: Re: implicit indexing on empty string
Post by: jef on October 14, 2014, 11:46:01 AM

~~Quote from: "Lutz"~~When these conflicts occur in newLISP, they are normally decided by the occurrance of real world usage patterns and their practicality rather then trying to be consistent.

Perfect, I see the point. Thanks for your detailed explanation!

newLISP Fan Club

Forum => newLISP in the real world => Topic started by: jef on October 13, 2014, 12:51:54 PM