Discussion:
(and scheme lisp) x Python and modern langs [was Re: gossip, Guy Steel, Lojban, Racket]
(too old to reply)
Xah Lee
2010-09-27 19:06:50 UTC
Permalink
2010-09-27
[x+1 for x in [1,2,3,4,5] if x%2==0]
map(lambda x:x+1,filter(lambda x:x%2==0,[1,2,3,4,5]))
How about this:

LC(func, inputList, P)

compared to

[func for myVar in inputList if P]

the functional form is:

? shorter
? not another idiysyncratic new syntax

--------------------

now, a separate issue. Suppose we want some ?list comprehension?
feature in a functional lang.
Normally, by default this can be done by

filter( map(func, inputList), Predicate)

but perhaps this usage is so frequent that we want to create a new
fuction for it, to make it more convenient, and perhaps easier to make
the compiler to optimize more. e.g.

LC(func, inputList, Predicate)

this is about whether a lang should create a new convenient function
that otherwise require 2 function combinations. Common Lisp vs Scheme
Lisp are the typical example of extreme opposites.

note, there's no new syntax involved.

--------------------

Now, let's consider another separated issue related to so-called ?list
comprehension?.
Suppose we decided that generating list by a filter is so frequently
used that it worth it to create a new func for it.

LC(func, inputList, Predicate)

Now, in functional langs, in general a design principle is that you
want to reduce the number of function unless you really need. Because,
any combination of list related functions could potentionally be a new
function in your lang. So, if we really think LC is useful, we might
want to generalize it. e.g. in

LC(func, inputList, Predicate)

is it worthwhile say to add a 4th param, that says return just the
first n? (here we presume the lang doesn't support list of infinite
elements) e.g.

LC(func, inputList, Predicate, n)

what about partition the list to m sublists?

LC(func, inputList, Predicate, n, m)

what about actualy more generalized partition, by m sublist then by m1
sublist then by m2 sublist?

LC(func, inputList, Predicate, n, list(m,m1,m2,...))

what about sorting? maybe that's always used together when you need a
list?

LC(func, inputList, Predicate, n, list(m,m1,m2,...), sortPredcate)

what if actually frequently we want LC to map parallel to branches?
e.g.

LC(func, inputList, Predicate, n, list(m,m1,m2,...), sortPredcate,
mapBranch:True)

what if ...

you see, each of these or combination of these can be done by default
in the lang by sequenceing one or more functions (i.e. composition).
But when we create a new function, we really should think a lot about
its justification, because otherwise the lang becomes a bag of
functions that are non-essential, confusing.

In summary:

? ?list comprehension? is a bad jargon.

? The concept of ?list comprehension? is redundant. There's no
justification for the concept to exist except historical.

? The syntax of ?list comprehension? in most lang is ad hoc syntax.

for those who find imperative lang good, then perhaps ?list
comprehension? is good, because it adds another idiosyncratic syntax
to the lang, but such is with the tradition of imperative langs. The
ad hoc syntax aids in reading code by various syntactical forms and
hint words such as ?[... for ... in ...]?.

Xah ? xahlee.org ?
namekuseijin
2010-09-27 19:11:20 UTC
Permalink
Post by Xah Lee
2010-09-27
[x+1 for x in [1,2,3,4,5] if x%2==0]
map(lambda x:x+1,filter(lambda x:x%2==0,[1,2,3,4,5]))
[snip]

how about this: read before replying.
Xah Lee
2010-09-27 21:39:56 UTC
Permalink
On 27 set, 16:06, Xah Lee <xah... at gmail.com> wrote:> 2010-09-27
[x+1 for x in [1,2,3,4,5] if x%2==0]
map(lambda x:x+1,filter(lambda x:x%2==0,[1,2,3,4,5]))
[snip]
how about this: ?read before replying.
hum???

i read your post quite carefully, and rather thought i replied well.
In fact, i really wanted to tell you ?read before replying? before but
refrained from making any of that expression.

here's 2 previous posts about list compre.
http://groups.google.com/group/comp.lang.lisp/msg/145f6ecf29ebbdaf
http://groups.google.com/group/comp.lang.lisp/msg/62ca84062c9fcdca

Xah
namekuseijin
2010-09-27 23:58:52 UTC
Permalink
Post by Xah Lee
On 27 set, 16:06, Xah Lee <xah... at gmail.com> wrote:> 2010-09-27
[x+1 for x in [1,2,3,4,5] if x%2==0]
map(lambda x:x+1,filter(lambda x:x%2==0,[1,2,3,4,5]))
[snip]
how about this: ?read before replying.
hum???
i read your post quite carefully, and rather thought i replied well.
I don't think so. You completely missed the point where I agreed
about filter map being more convenient when calling predefined
functions and also the detailed explanation of why do in scheme is not
imperative at all.
Xah Lee
2010-09-28 17:56:55 UTC
Permalink
in anycase, how's ?do? not imperative?
how's ?do? a ?named let?? can you show example or reference of that
proposal? (is it worthwhile?)
"
(do ((i 0 (+ 1 i)) ?; i initially 1, (+ 1 i) at each "step"
? ? ?(r 0 (+ i r))) ; r initially 0, (+ i r) at each "step"
? ((> i 5) r)) ? ? ?; when i>5, return r
=> 15
(let loop ((i 0)
? ? ? ? ? ?(r 0))
? (if (> i 5) r
? ? (loop (+ 1 i) (+ i r))))
=> 15
((lambda (loop)
? ?(loop loop 0 0))
?(lambda (loop i r)
? ?(if (> i 5) r
? ? ? ?(loop loop (+ 1 i) (+ i r)))))
=> 15
which, as you can see, is merely function application. ?There's
nothing there except evaluation of arguments, application of arguments
to function and function return. ?It's not because they chose `do', or
`for' or `while' for naming such syntax, that it behaves the same as
their imperative homographs."
as i said, regarding do: ?do? in general in any lang is simply
impreative. We don't even have to know the details. I don't care
whatnot fuck proposal from whatnot lisp of what's actually going on.
If it is named ?do?, it is imperative.
It's not: ?one can name factorial do. ?It's just a name. ?Who doesn't
like do? ?It's short, to the point...
ultimately, all lang gets transformed at the compiler level to become
machine instructions, which is imperative programing in the ultimate
sense.

You say that ?do? is merely macro and ultimately function application.
But to what level should we go down this chain on how the language
actually works when evaluating a function in source code?

any functional lang, quickly becomes imperative when compiled to some
intermediate code or interpreted. In a sense, it can't be any other
way. Functions are abstract mathematical ideas, while ?do? loop or any
instruction are actual steps of algorithms.

Xah ? xahlee.org ?
Xah Lee
2010-09-28 22:38:23 UTC
Permalink
2010-09-28
Post by Xah Lee
ultimately, all lang gets transformed at the compiler level to become
machine instructions, which is imperative programing in the ultimate
sense.
You say that ?do? is merely macro and ultimately function application.
But to what level should we go down this chain on how the language
actually works when evaluating a function in source code?
any functional lang, quickly becomes imperative when compiled to some
intermediate code or interpreted. In a sense, it can't be any other
way. Functions are abstract mathematical ideas, while ?do? loop or any
instruction are actual steps of algorithms.
That is true as of Mathematica too. ?Difference being that do in
scheme is pretty-much user-level syntax. ?If you look in most (good)
implementations sources, do and let are defined in scheme itself, not
C or lower-level: ?C code only deals with transforming lambda
application and tail calls into proper gotos.
So, as far as we're talking about scheme, haskell or Mathematica code,
it's all functional in its abstraction context.
do syntax does allow for imperative commands to be issued in scheme,
just like let. ?It does not mean it was used in said examples nor that
do is automatically inherently imperative just because of choice of
name. ?imperative do -> (do (steppers ...) (final-condition? result)
malign-imperative-code-here ...)
so, now that we got it clear why do in scheme is not (inherently)
imperative why were you bashing useful (at times) functional syntax in
the form of list comprehensions again?
le's get precise. The argument i want to make, is this:

? ?list comprehension? is a very bad jargon; thus harmful to
functional programing or programing in general. Being a bad jargon, it
encourage mis-communication, mis-understanding.

? ?list comprehension? is a redundant concept in programing. The
concept is of historical interest. e.g. when people talk about the
history of computer languages. The LC can simply be filter(map(func,
list), predicate).

? The special syntax of ?list comprehension? as it exists in many
langs, are not necessary. It can simply be a plain function, e.g
LC(function, list, filter).

I gave a stand-alone explanation of these points at:
http://groups.google.com/group/comp.lang.lisp/msg/329b3b68ff034453

Do you disagree or agree with the above?

This is the point _I_ want to argue about, but you don't seem to admit
any part of it, but you seems to want to discuss about ?do? in Scheme
lisp being functional.

So, perhaps we can now focus on this subject:

The ?do? in Scheme lisp is not imperative, or, it can be considered as
functional.

Alright. To be honest, i haven't had enough experience to comment on,
but in general, i understand the example you've given, and i disagree.

Full report on your argument on this is given at:
http://groups.google.com/group/comp.lang.lisp/msg/87a987070e80231f

Now, in your message (quoted above), you made further argument on
this. I think the main point is this, quote:

?do syntax does allow for imperative commands to be issued in scheme,
just like let. It does not mean it was used in said examples nor that
do is automatically inherently imperative just because of choice of
name. imperative do -> (do (steppers ...) (final-condition? result)
malign-imperative-code-here ...)?

i don't think your argument is forceful enough.

It appears that by this argument you even say that ?let? is not
functional.

Here, the issue verges on what is functional? What is a function? If a
function in lisp is defined as macro, does it ceases to be considered
as a function? Likewise, if a lisp's has ?for? loop that is defined as
a macro, is that ?for? now considered a function?

this is getting quite iffy. What level or aspect are we considering?
In each lang, usually they define certain terms specifically to the
lang, and to various degree of precision. For eample, the term
?object? means very different things in a technical way in different
langs. Same for the word ?function?, ?keyword?, ?command?, ?module?,
?package? ...

So, overall, i consider your argument for ?do? in Scheme lisp being
functional is weak, or trivial. It seems to be a pet peeve. You got
annoyed because i seem to have ignored it entirely. But i got annoyed
by you because you don't get the point about what i consider more
significant opinion on ?list comprehension?, which you totally ignored
and kept at hacking the ?do? in Scheme lisp.

Xah ? xahlee.org ?
namekuseijin
2010-09-29 18:02:03 UTC
Permalink
Post by Xah Lee
? ?list comprehension? is a very bad jargon; thus harmful to
functional programing or programing in general. Being a bad jargon, it
encourage mis-communication, mis-understanding.
I disagree: it is a quite intuitive term to describe what the
expression does.
Post by Xah Lee
? ?list comprehension? is a redundant concept in programing. The
concept is of historical interest. e.g. when people talk about the
history of computer languages. The LC can simply be filter(map(func,
list), predicate).
I agree it is redundant. Like pretty much all syntax: all one needs
is a way to define functions and to apply function to arguments (or
assignment and pre-defined loops for imperative folks). Syntax may
still be more convenient, though.

Which is strange since you were an ardent syntax lover a few
iterations ago.
Post by Xah Lee
? The special syntax of ?list comprehension? as it exists in many
langs, are not necessary. It can simply be a plain function, e.g
LC(function, list, filter).
I disagree. Syntax may be redundant, but it is there to be
convenient.

I'll quote it again:
"For instance, this is far more convenient:
[x+1 for x in [1,2,3,4,5] if x%2==0]
than this:
map(lambda x:x+1,filter(lambda x:x%2==0,[1,2,3,4,5]))

but on the other hand, this is more convenient:
map(inc,filter(evenp,[1,2,3,4,5]))

(ignoring the lines of code for inc and evenp, of course. But as
long
as they are used in many parts, it *is* more convenient)

In short, list comprehensions are useful syntatic expressions
returning lists as long as you don't care for the short functions
used
in them."
Post by Xah Lee
?do syntax does allow for imperative commands to be issued in scheme,
just like let. It does not mean it was used in said examples nor that
do is automatically inherently imperative just because of choice of
name. imperative do -> (do (steppers ...) (final-condition? result)
malign-imperative-code-here ...)?
i don't think your argument is forceful enough.
It appears that by this argument you even say that ?let? is not
functional.
In the case of Lisps, it depends on context: let is an expression
returning a value, but Lisps are not purely functional languages and
you *may* use imperative statements in the body, resulting in useful
side-effect computations.

That's why I said do is no more imperative than let: 1) because it
*is* let and 2) because Lisps *allow* imperative constructs in the
body of lambdas. do is not inherently imperative in the same sense
Lisp/Scheme is not inherently imperative: they allow you to do purely
functional evaluation of expressions but also to tint the computations
with side-effects... your choice.
Post by Xah Lee
So, overall, i consider your argument for ?do? in Scheme lisp being
functional is weak, or trivial. It seems to be a pet peeve.
It is a pet peeve in that you call `do' imperative without arguments
while a few other Schemers call `do' imperative on the basis of
political bickering. Nobody gives `do' a chance of the base of it
being what it is: a macro transform into let. Any imperative
programming you do with `do' will get the same effect as if you do the
same imperative programming with let. Imperative or functional, it's
up to the user, not inherently from any language construct.
Post by Xah Lee
You got
annoyed because i seem to have ignored it entirely. But i got annoyed
by you because you don't get the point about what i consider more
significant opinion on ?list comprehension?, which you totally ignored
and kept at hacking the ?do? in Scheme lisp.
It's because I don't think I have much to comment on list
comprehensions other than being useful syntax at times for an
expression returning a list.
Xah Lee
2010-09-29 20:46:08 UTC
Permalink
Post by Xah Lee
? ?list comprehension? is a very bad jargon; thus harmful to
functional programing or programing in general. Being a bad jargon, it
encourage mis-communication, mis-understanding.
I disagree: ?it is a quite intuitive term to describe what the
expression does.
what's your basis in saying that ?list comprehension? is intuitive?

any statics, survery, research, references you have to cite?

to put this in context, are you saying that lambda, is also intuitive?
?let? is intuitive? ?for? is intuitive? ?when? is intuitive? I mean,
give your evaluation of some common computer language termilogies, and
tell us which you think are good and which are bad, so we have some
context to judge your claim.

For example, let us know, in your view, how good are terms: currying,
lisp1 lisp2, tail recursion, closure, subroutine, command, object. Or,
perhaps expound on the comparative merits and meaning on the terms
module vs package vs add-on vs library. I would like to see your view
on this with at least few paragraphs of analysis on each. If you, say,
write a essay that's at least 1k words on this topic, then we all can
make some judgement of your familiarity and understanding in this
area.

Also, ?being intuitive? is not the only aspect to consider whether a
term is good or bad. For example, emacs's uses the term ?frame?. It's
quite intuitive, because frame is a common english word, everyone
understands. You know, door frame, window frame, picture frame, are
all analogous to emacs's ?frame? on a computer. However, by some turn
of history, in computer software we call such as ?window? now, and by
happance the term ?window? also has a technical meaning in emacs, what
we call ?split window? or ?pane? today. So, in emacs, the term ?frame?
and ?window? is confusing, because emacs's ?frame? is what we call
?window?, while emacs's ?window? is what me might call a pane of a
split window. So here, is a example, that even when a term is
intuitive, it can still be bad.

as another example, common understanding by the target group the term
is to be used is also a important aspect. For example, the term
?lambda?, which is a name of greek char, does not convey well what we
use it for. The word's meaning by itself has no connection to the
concept of function. The char happens to be used by a logician as a
shorthand notation in his study of what's called ?lambda
calculus? (the ?calculus? part is basically 1700's terminology for a
systematic science, especially related to mechanical reasoning).
However, the term ?lambda? used in this way in computer science and
programing has been long and wide, around 50 years in recent history
(and more back if we trace origins). So, because of established use,
here it may decrease the level of what we might think of it as a bad
jargon, by the fact that it already become a standard usage or
understanding. Even still, note that just because a term has establish
use, if the term itself is very bad in many other aspects, it may
still warrant a need for change. For one example of a reason, the
argon will be a learning curve problem for all new generations.

You see, when you judge a terminology, you have to consider many
aspects. It is quite involved. When judging a jargon, some question
you might ask are:

? does the jargon convey its meaning by the word itself? (i.e. whether
the jargon as a word is effective in communication)

? how long has been the jargon in use?

? do people in the community understand the jargon? (e.g. what
percentage)

each of these sample questions can get quite involved. For example, it
calls for expertise in linguistics (many sub-fields are relevant:
pragmatics, history of language, etymology), practical experience in
the field (programing or computer science), educational expertise
(e.g. educators, professors, programing book authors/teachers),
scientific survey, social science of communication...

also, you may not know, there are bodies of professional scientists
who work on terminologies for publication. It is not something like ?O
think it's good, becus it is intuitive to me.?.

I wrote about 14 essays on various jargons in past decade. You can
find them on my site.

i removed your arguments on other parts about ?list comprehension?,
because i didn't find them valuable. (barely read them) However, i
appreciate your inputs on the ?do? in Scheme lisp has a functional
usage, and some other misc chat info from the beginning of this thread
on comp.lang.lisp.

Xah ? xahlee.org ?
Ian Kelly
2010-09-29 21:48:06 UTC
Permalink
Post by Xah Lee
what's your basis in saying that ?list comprehension? is intuitive?
any statics, survery, research, references you have to cite?
to put this in context, are you saying that lambda, is also intuitive?
?let? is intuitive? ?for? is intuitive? ?when? is intuitive? I mean,
give your evaluation of some common computer language termilogies, and
tell us which you think are good and which are bad, so we have some
context to judge your claim.
For example, let us know, in your view, how good are terms: currying,
lisp1 lisp2, tail recursion, closure, subroutine, command, object. Or,
perhaps expound on the comparative merits and meaning on the terms
module vs package vs add-on vs library. I would like to see your view
on this with at least few paragraphs of analysis on each. If you, say,
write a essay that's at least 1k words on this topic, then we all can
make some judgement of your familiarity and understanding in this
area.
Have you actually written an essay on this topic of the sort that you are
requesting here? I googled your site, but all I could find was your
Perl-Python tutorial in which you simply stated that "This construct has
acquired a [sic] incomprehensible name 'list comprehension' in computing
industry and academia."

The obvious pun aside, I don't understand why you find the name to be
incomprehensible. All it means is that the list is being defined by
comprehension (i.e. intension) in the logical sense, as opposed to the more
common extensive definition (e.g. myList = [1, 2, 3]). The suggestion that
this nomenclature is any more obscure than "lambda", in either origin or
industry, is dubious to me.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-list/attachments/20100929/70084dc5/attachment.html>
namekuseijin
2010-09-30 03:28:35 UTC
Permalink
Post by Xah Lee
Post by Xah Lee
? ?list comprehension? is a very bad jargon; thus harmful to
functional programing or programing in general. Being a bad jargon, it
encourage mis-communication, mis-understanding.
I disagree: ?it is a quite intuitive term to describe what the
expression does.
what's your basis in saying that ?list comprehension? is intuitive?
it generates a list from syntax comprehended in list-like syntax!
Post by Xah Lee
any statics, survery, research, references you have to cite?
how about common sense?
Post by Xah Lee
to put this in context, are you saying that lambda, is also intuitive?
No.
Post by Xah Lee
?let? is intuitive?
yes, it's focking everyday term used in the same way: let this be
this and that be that and thus...
Post by Xah Lee
?for? is intuitive?
yes, it's focking everyday term used in the same way: for this and
this and this do that...
Post by Xah Lee
?when? is intuitive?
when this, then that?

common sense, Xah!
Post by Xah Lee
For example, let us know, in your view, how good are terms: currying,
lisp1 lisp2, tail recursion, closure, subroutine, command, object.
These terms have a technical meaning coming from historic events in
the areas they are used. It's like that in all areas, you may also
bash medicine jargon if you want.

Though subroutine, command and object are pretty intuitive by common
sense alone.
Post by Xah Lee
perhaps expound on the comparative merits and meaning on the terms
module vs package vs add-on vs library. I would like to see your view
on this with at least few paragraphs of analysis on each.
They are all the same shit. These were developed by managers and
buzzwriters... ;)
Post by Xah Lee
Also, ?being intuitive? is not the only aspect to consider whether a
term is good or bad. For example, emacs's uses the term ?frame?. It's
quite intuitive, because frame is a common english word, everyone
understands. You know, door frame, window frame, picture frame, are
all analogous to emacs's ?frame? on a computer. However, by some turn
of history, in computer software we call such as ?window? now, and by
happance the term ?window? also has a technical meaning in emacs, what
we call ?split window? or ?pane? today. So, in emacs, the term ?frame?
and ?window? is confusing, because emacs's ?frame? is what we call
?window?, while emacs's ?window? is what me might call a pane of a
split window. So here, is a example, that even when a term is
intuitive, it can still be bad.
emacs is all FUBAR in more than one way. being intuitive is not
exactly what it is known for... ;)

well, I shouldn't be bashing it, my vim is not that funky among
commoners anymore anyway... :p
Post by Xah Lee
I wrote about 14 essays on various jargons in past decade. You can
find them on my site.
yeah, I've read them once in a while...
Seebs
2010-09-30 03:48:06 UTC
Permalink
Post by namekuseijin
it generates a list from syntax comprehended in list-like syntax!
Okay, help me out here. (Killed the crossposting.)

I am not understanding how the word applies. I'm fine with it, but I don't
see any relation at all between the thing called a list comprehension and
the word "comprehension" as I normally understand it.

Who or what is doing the comprehending? Is this a sense of "comprehension"
other than "to understand"? It seems like it's perhaps related to
"comprehensive". However, I've never seen "comprehension" used to refer
to anything other than understanding prior to encountering "list
comprehensions".

[... hmm. maybe time to go searching...]

Looking around, it seems this is from mathematical jargon, to wit,
"set comprehensions". Since I hadn't run into that jargon, I had no
clue what the etymology was, and "comprehended" is not a verb I would
ever have used with this. However, looking around, it appears that
this usage also occurs in the same jargon; once you've got one of them
the other follows.

I guess the key, though, is that this is purely jargon, and jargon from
another field -- not all programmers have done all mathematics. I even
took a ton of bonus math in college, but happened not to have done anything
where this terminology was used. So the usage is, pardon the pun,
incomprehensible to me to begin with, and saying it's called a
comprehension because it's comprehended doesn't help -- that's two forms
of the same unfamiliar jargon.

Of course, the jargon is pretty reasonable as such goes, in no small
part because of the plain English sense of "comprehensive" in the
sense of covering something completely, so it's not awful.

But from where I'm coming, it would be every bit as obvious to call it
a "list exhaustion", by analagous derivation from "exhaustive".

-s
--
Copyright 2010, all wrongs reversed. Peter Seebach / usenet-nospam at seebs.net
http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!
I am not speaking for my employer, although they do rent some of my opinions.
Continue reading on narkive:
Loading...