6 May
2017
6 May
'17
12:07 p.m.
On Sat, 06 May 2017 12:16:53 +1000 Noel Hunt <noel.hunt(a)gmail.com> wrote:
What you call 'composability' is nothing more than the 'software
tools' approach.
Composable components can have a much tigher coupling. vi,
rsync, git and gdb are s/w tools but they are not composable
in the sense of sed, grep, uniq, awk, head, tail, tr, sort,
ls, find etc.
I recall reading an interview with Dennis Ritchie, but
can no
longer find it, where he talks about this approach versus the
monolithic program model, as for example demonstrated by
'perl', which does everything. Dennis remarked that the
'tools' approach required careful thought (which programs to
use, how to connect them with pipes) and so was more difficult
to use, hence the popularity of 'perl'.
This is the "modularity" approach, where one program does one
thing well rather than doing everything (e.g IDE). But
moudlarity does not necessarily give you composability.
Also, it is not enough to have composable components; you need
a language/environment in which they can be used.
A most beautiful example of this approach is from Doug
McIlroy
in his critique of Donald Knuth's solution to a problem posed
by Jon Bentley in his 'Programming Pearls' column:
Read a file of text, determine the n most frequently used
words, and print out a sorted list of those words along with
their frequencies.
Donald Knuth wrote a long, beautifully crafted program in some
pseudo-code. Doug McIlroy provided an alternative solution:
tr -cs A-Za-z '\n' |
tr A-Z a-z |
sort |
uniq -c |
sort -rn |
sed ${1}q
This is real genius.
Indeed.
Note that a similar approach was implemented by Iverson in
APL. In fact a shell pipeline has a lot in common with array
programming!
Iverson in essence built a whole workshop with a set of simple
but powerful standard tools (functions and higher order
functions). The same has been carried on in follow on array
languages such as j and k and q languages. Many of these
array functions are directly applicable to stream processing.
In contrast unix shells provide a very shallow glue layer.
On Sat, May 6, 2017 at 1:37 AM, Bakul Shah
<bakul(a)bitblocks.com> wrote:
> I think the key issue is not as much minimalism as composability. BSD
> often prioritized convenience over composability. Each command doing one
> thing well and doing line oriented makes them more composability. You can
> always package up convenient combinations in a script. Plan9 has lc which
> prints like unix ls -C but it is an rc script. Trying to achieve
> composability can result in leaner systems.