OpenEuphoria

Re: Stepwise Refinement

• Posted by "M. Ter Haseborg" <M.S.ter.Haseborg at FWN.RUG.NL> Sep 19, 2000
• 451 views

Hai David

There is a good book about this subject (and also a language
called Elan) . You can find it on ftp.cs.kun.nl/pub/elan

Menno

Date sent:              Tue, 19 Sep 2000 00:04:47 -0700
Send reply to:          Euphoria Programming for MS-DOS <EUPHORIA at
LISTSERV.MUOHIO.EDU>
From:                   David Cuny <dcuny at LANSET.COM>
Subject:                Stepwise Refinement
To:                     EUPHORIA at LISTSERV.MUOHIO.EDU

> One feature I've not seen in many languages, but is occasionally useful, it
> that of subfunctions that directly support stepwise refinement of routines.
> Here's an example from the ABC language:
>
>  HOW TO RETURN index doc:
>     PUT {} IN where
>     FOR line.no IN keys doc:
>        TREAT LINE
>     RETURN where
>  TREAT LINE:
>     FOR word IN split doc[line.no]:
>        IF word not.in keys where:
>          PUT {} IN where[word]
>        INSERT line.no IN where[word]
>
> Any language that thinks 'HOW TO RETURN' is better than 'FUNCTION' deserves
> to die a quick death (as ABC did), but that's not the point here. The
> support function TREAT LINE shares the local variables with the main
> routine; it's *exactly* the same as:
>
>  HOW TO RETURN index doc:
>     PUT {} IN where
>       FOR line.no IN keys doc:
>       FOR word IN split doc[line.no]:
>          IF word not.in keys where:
>            PUT {} IN where[word]
>          INSERT line.no IN where[word]
>     RETURN where
>
> Yes, I know the basic premise of Euphoria is to stay small, prevent feature
> creep, and so on. On the other hand, there are quite a number of times when
> routines have grown so large they are horribly bloated, but splitting them
> up requires creating module variables or awkward forward references. For
> example:
>
>    procedure parse()
>       if is("function") then  parse_function()
>       elsif is("procedure") then parse_procedure()
>       ...
>       end if
>    end procedure
>
> The helper procedures here (parse_function, parse_procedure, etc) often need
> to refer back to parse, which requires that it be a forward reference. In
> fact, if often requires a host of forward references. In addition, since
> these sorts of routines are often recursive, which makes the use of local
> variables even more useful.
>
> Since Python (the successor of ABC) doesn't include this sort of feature,
> it's not clear that the author considered successive refinement a winning
> feature. Still, I think it's worth considering adding to Euphoria.
>
> -- David Cuny