coding style

[p da]

I was reading code of 4th libraries just for fun when I discovered this:

\ Must define the 'NotFound' for interprt.4th
:noname 2drop ." Not found!" cr ; is NotFound

And I wonder what is the difference of writing simply this way:

: NotFound 2drop ." Not found!" cr ; 

As far as I know ":noname" lets a xt in the stack and "is" assign a token to a deferred word, so they both should be equivalent.   The only reason I can imagine to do that way is NotFound being a deferred word by default so the only way to set it is using "is" and you cannot redefine it, but I suppose you can redefine every word in 4th.

greets

[The Beez]

Yes, you're right - they're equivalent. 

Except for one thing: you can redefine the former, you cannot redefine the latter without a messy HIDE directive and a complete redefinition. And - very important - all previous calls would be invalidated.

Your solution works fine for a template like CONVERT.4TH - but not for a library. And yes, this "redefinition thingy" is actually used in the repository:

dc.4th:       :noname #UndefName throw ; is NotFound \ standard 'abort' word
editor.4th:   :noname #UndefName throw ; is NotFound \ for interpret library

euro.4th:     :noname ." Unknown command '" type ." '" cr ; is NotFound
ipsubnet.4th: :noname ." Unknown command '" type ." '" cr ; is NotFound
sudoku.4th:   :noname ." Unknown command '" type ." '" cr ; is NotFound

filer.4th:    :noname oops throw ; is NotFound       ( --)
spiles.4th:   :noname oops throw ; is NotFound       ( --)

There are a few programs that repeat the original definition - but it's not required, as skyquery.4th and topitsm.4th prove. These programs use the default definition.

And yes, you can redefine any word in 4tH - but not as liberally as in vanilla Forth. It requires the "HIDE" word. And previous calls are not converted - so these will always defer to the original definition.

You can compare a "DEFER"red word best as a VALUE containing an execution token (function pointer), followed by an EXECUTE. And since a VALUE is a variable, the address it jumps to is dependent on what the variable contains. In short - change the variable, change the location it jumps to. It's as easy as that.

Hans Bezemer