From: ruvim.pinka@gmail.com   
      
   On 2024-10-12 17:54, Ruvim wrote:   
   > 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 )   
      
   I do not like these names too.   
      
   These seem better:   
      
        ?NZ-DROP   
        ?ZE-DROP   
      
      
   >   
   >   
   >> : ?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  ForthHub/discussion/discussions/171#discussioncomment-10882259>   
   >   
   > (this can be discussed there, or in a new thread here)   
   >   
   >   
   >   
   > --   
   > Ruvim   
   >   
      
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