RE: [stack] various questions

wtanksley@bigfoot.com — 2000-05-11 16:38:01

From: peter_easthope@...



 >Sorren, why are you creating a new language and 

>writing the compiler?  If you have explained already 

>perhaps you can just point me back to the message.



 
I couldn't say why he's doing it, but I am first because I want to

understand more about this new 



 >Have any of you folks used J?  The concatination here

>is reminiscent of J.



 
Used it, loved it.  It's not in the least concatenative.  It is, however,

combinative, and all concatenative languages I know of are also combinative.



 >wtanksley@... said,

>wt> the syntax I used depended on strings, while 

>wt> yours depends on "symbols". 



>I know what a string is.  What is a "symbol"?



 
Doesn't really matter.  A symbol is a way of economically and quickly

expressing a token which is similar to the ones which the language uses for

identifying functions.  In Postscript, you express a symbol by preceding it

by a backslash.



 >Brent Kirby mentioned,

>bk> Count upward, beginning at 0, skipping multiples of five



>Sorren replied,

>sr> 0 [dup 5 % 0 = [dup puti] [] if 1 +] spin



>In case anyone is interested, this is it in J without division.

>J evaluates each line from right to left. (OK, it wasn't my 

>choice.)



 
It's a brilliant convention.  It allows the programmer to know exactly what

order things are going to happen in without making parsing hard.



 >wt> ... more thinking about continuations. 

>What is a continuation?



 
Well, think of how a function gets called and later on returns to its

caller.  Suppose instead of always returning to its caller, it was possible

to return to something else.  That's a continuation; it's the ability to

formally change the return address.



 >Thanks,       Peter E.



 
-Billy

wtanksley@bigfoot.com — 2000-05-11 16:44:12

From: wtanksley@... [mailto:wtanksley@...]



 >From: peter_easthope@...



>>Sorren, why are you creating a new language and 

>>writing the compiler?  If you have explained already 

>>perhaps you can just point me back to the message.



>I couldn't say why he's doing it, but I am first because I want to

>understand more about this new 



 
...theory of language.  I've always liked Forth, and always wondered why

such a functionally impure language was so easy to code in, almost as though

it were functionally pure.



Now, thanks to the Joy pages, I discover that there _is_ a functional theory

which explains Forth.



-Billy

peter_easthope@gulfnet.pinc.com — 2000-05-11 18:04:19

Billy said,

wt> It's [J is] not in the least concatenative.  It is, however,

combinative, and all concatenative languages I know of are also combinative.



Why do you call (+/ @ *:) combination rather than 

concatenation of  "sum over" and square?



Thanks,       Peter E.

 

peter_easthope@...   48.7689d N, 123.3017d W, 30 m

Recommended reading:  http://www.naturalstep.org/

wtanksley@bigfoot.com — 2000-05-11 19:28:48

From: peter_easthope@...



 >Billy said,

>wt> It's [J is] not in the least concatenative.  It is, however,

>wt> combinative, and all concatenative languages I know of are 

>wt> also combinative.



>Why do you call (+/ @ *:) combination rather than 

>concatenation of  "sum over" and square?



 
A language may use and provide concatenation without being concatenative.

For example, C provides strcat.  Lisp provides cons (and concat).  Yet none

of these are in the least concatenative languages, because none of these

languages operate by treating concatenation of functions as their

composition.



Monadic functions in J behave in a concatenative manner, using an array

rather than a stack, although the language still behaves applicatively and

therefore requires a parser.  Dyadic functions do not behave

concatenatively.



 >Thanks,       Peter E.



 
-Billy

peter_easthope@gulfnet.pinc.com — 2000-05-11 20:19:29

Billy said,

wt> It's [J is] not in the least concatenative.  It is, however,

combinative, and all concatenative languages I know of are also combinative.



Why do you call (+/ @ *:) combination rather than 

concatenation of  "sum over" and square?



Thanks,       Peter E.

 

peter_easthope@...   48.7689d N, 123.3017d W, 30 m

Recommended reading:  http://www.naturalstep.org/

wtanksley@bigfoot.com — 2000-05-11 20:57:36

From: peter_easthope@...



 >Billy said,

>wt> It's [J is] not in the least concatenative.  It is, however,

>wt> combinative, and all concatenative languages I know of are 

>wt> also combinative.



>Why do you call (+/ @ *:) combination rather than 

>concatenation of  "sum over" and square?



 
(I just recieved this for the second time -- I'm not sure why.)



By the way, I don't call that "combination". you misunderstood my use of the

overloaded word "combinative".  In this context that does not talk about a

specific operation which combines two things, nor about the branch of

mathematics which counts the number of combinations of things, but rather

about the class of functions which act by taking more than one item of data

and producing a new arrangement of that data.



For example, SWAP is a combinator; it takes two parameters and produces two

parameters in a different order.  DROP is also a combinator, although a

special one (since it destroys data).  (Joy calls this function "pop", but I

find that name abyssimally hard to remember, partly out of old habit and

partly because that implies to me that the data is being preserved

somewhere.)



 >Thanks,       Peter E.



 
-Billy