Re: Elegant code Was: Re: what kind of non microconroller app are

Jonah Thomas wrote:
 > [...]
 > I want to ask anyone who's interested about a programming puzzle I ran
 > into when I tried something similar.
 >
 > The idea is to have a routine GOOD-STRING that accepts a string ( ca
len
 > ) and an execution token that acts on the string and checks the first
 > part of the string for some condition. Like, it couild test whether a
 > character is an uppercase letter, or whether it's a digit, or
 > alphanumeric, or whether two characters are ":=" or whatever. The
 > execution token should accept an address in the string, and it returns
a
 > flag.
 >
 > XT ( ca -- flag )
 >
 > The routine does ( ca len xt -- ca len' ) . It returns as much of the
 > string as meets the condition the execution token tests for.
 >
 > So I'd wind up with:
 >
 > : STRING-CHECKER ( S: xt "name" -- )
 > ( child: ca len -- ca len' )
 >    CREATE ,
 >    DOES> @[EMAIL PROTECTED]
 GOOD-STRING ;
 >
 > to make a collection of named routines to check strings in various
ways.
 >
 > My first attempt at GOOD-STRING was like this:
 >
 > : GOOD-STRING1 ( S: ca len xt -- ca len' )
 >    >R
 >    2DUP BEGIN
 >      DUP 0 > WHILE
 >        OVER R@[EMAIL PROTECTED]
 EXECUTE WHILE
 >          1 /STRING
 >      REPEAT
 >    THEN
 >    NIP - RDROP ;

 > [improvement iterations]

Like Gerry, I think this first attempt looks fine.

Here's a similar approach, from a translator I've stopped
working on for the time being.

: make-recog  ( "name" xt -- )
   ---
     Define a word that executes the "is" string test procedure
     xt, leaving true if so, else false and the string.  The
     stack pattern for the procedure is

       ( s -- after.s is.s true | s false )

     where is.s is the part of the input string up to the
     character where it fails to "be-a", and after.s is the rest
     of the string, including that character.  In the true case,
     it is assumed that is.s cannot be empty.
   ---
   create ,
DOES>  ( s -- after.s true | s false )
   @[EMAIL PROTECTED]
 ( after.s is.s true | s false)
   IF   ( is.s) sdrop ( after.s) true
   ELSE ( s) false THEN ;

The "is" recognition procedures are coded as C primitives, in a
pfe loadable module.  SDROP is an alias for 2drop, "s" and "x.s"
stand for ANS Forth strings, and --- is a multiline comment
word.

-- David