Undefined values: Difference between revisions

=={{header|PicoLisp}}==

An internal symbol is initialized to NIL. Depending on the context, this is

interpreted as "undefined". When called as a function, an error is issued:

<lang PicoLisp>: (myfoo 3 4)

!? (myfoo 3 4)

myfoo -- Undefined

?</lang>

The function 'default' can be used to initialize a variable if and only

if its current value is NIL:

<lang PicoLisp>: MyVar

-> NIL

: (default MyVar 7)

-> 7

: MyVar

-> 7

: (default MyVar 8)

-> 7

: MyVar

-> 7</lang>