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From: Ruvim <ruvim.pinka@gmail.com>
Newsgroups: comp.lang.forth
Subject: Re: Number parsing with checks
Date: Sat, 12 Oct 2024 17:54:45 +0400
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On 2024-10-12 05:45, dxf wrote:
> The basics:
> 
> : .BAD ( -- )  cr ." Invalid item"  .abort ;
> 
> : ZE? ( x -- )  if .bad then ;     \ abort if non-zero
> : NZ? ( x -- )  0= ze? ;           \ abort if zero

Typically, if word name ends with a question mark, the first (top) 
output parameter of the word is a *flag*. And it's true for all standard 
words. (though, opposite is not true)

These are better names and narrower stack diagrams:

   DROP-NZ ( x\0 --  |  0 -- never )
   DROP-ZE ( 0 --  |  x\0 -- never )


> : ?ZE ( x -- x )  dup ze? ;        \ check x is zero
> : ?NZ ( x -- x )  dup nz? ;        \ check x is non-zero

Better stack diagrams:

   ?ZE ( 0 -- 0  |  x\0 -- never )
   ?NZ ( x.some\0 -- x.some  |  0 -- never )

I suggest to use the data type symbol "never" for the empty data type.

See my explanation about the empty data type at 
<https://github.com/ForthHub/discussion/discussions/171#discussioncomment-10882259>

(this can be discussed there, or in a new thread here)



--
Ruvim