integer conversions

[nigelbrown]

currently:



> (integer 1)

1

> (integer "")

nil

> (integer nil)

missing argument in function integer

> (integer unbound 0)

value expected in function integer : nil

> (integer nil 0)

missing argument in function integer





Why are (integer nil 0) and (integer unbound 0) handled differently?



Lutz - would you consider allowing integer to return the default if the argument is nil? (would just tidy up some of my code - currently I check for nil prior to conversion).

[Lutz]

In 7.5.15 if the datatype is not a string or a number in integer or float, then nil will be returned or the default value if specified:



(integer nil) => nil

(integer nil 0) => 0



(float nil) => nil

(float nil 0) => 0



previously this caused error messages



Lutz

[newdep]

This is intresting actualy, in newlisp 'nil is not represented with a

value conresponding 0. So 'nil could also be intepreted as being true or 1.



(> 1 nil)  works so that assumes 'nil equals 0.



(= nil 0) says 'nil, which means 'nil is string and 0 is number.



Its sometimes confusing using 'nil, therefor i currently bypass it

and only use it as a return handler in functions.

[Lutz]

The reason that (> 1 nil) returns 0 is that the comparison operator compares datatypes when the arguments are not equal different types (see the manual).



nil and 0 have nothing to do with each other!



nil is a boolean value and a symbnol nothing else. The expressions:



(integer nil 0) => 0 ; in version 7.5.15

(integer nil 123) => 123 ; in version 7.5.15

(integer 'abc 999) => 999

;;

(float nil 0) => 0 ; in version 7.5.15

(float nil 123) => 123 ; in version 7.5.15



will return the default value,



Lutz

[newdep]

yes your right about 'nil, still is funny to get confused about the meaning

of 'nil and 'null or even 0 , which are not the same :-)

[Lutz]

Some programming languages take 0 as a boolean false in a boolean context (like 'C') , but this is not the case in newLISP, where only nil and the empty list () are taken as boolean false in a boolean context:



(if 0 'yes 'no) => yes



(if () 'yes 'no) => no



Lutz