A Joeish Erlang distribution (long)

[Joe Armstrong]

On Mon, 27 Jan 2003, Vance Shipley wrote:

> On Mon, Jan 27, 2003 at 05:32:33PM +0100, Kenneth Lundin wrote:
> }  
> }  Here are some comments from the Erlang/OTP Product Manager at Ericsson.
> }  
> }  1) We have plans to divide the Erlang/OTP distribution into s number of
> }  separate packages. Preliminary we are thinking of 3 packages:
> }  - Core package (erts,kernel,stdlib,sasl,mnesia,os_mon,inets,compiler,..)
> }  - Tools&Utilities (parse_tools, tools, debugger, observer, et, tv, ...
> }  - Telecom/protocols (snmp, asn1, orber, megaco, ...
> 
> I would suggest that the core package be even more limited.  All you really
> need to run Erlang is erts, kernel and stdlib.  A "Development" package 
> would be appropriate.  If you think in terms of embedded systems and what
> they require it makes a cleaner seperation.

  I  entirely agree  - snmp  mensia etc  are *applications  that are
written in Erlang - they should not therefore be in the core release.

  The core should be:

	1) The compiler 
	2) The run time
	3) A minimal set of libraries to do something "useful"

  Think C - a minimal set of stuff is

	- A compiler that runs "out of the box"
	- A minimal set of libraries (libc) so you can do something.

  IMHO we should have:

	- A compiler that runs "out of the box"
	- Minimal library support
	  Somewhere you have to "draw the line" 

	My "minimal support" really means device drivers - so support
for files, sockets, binary filers, ... etc. is in - everything else is out.
also ets is so low level that it can be considered "part of the language"

   We have to be pragmatic as well so I'd include

	- dets
	- dynamic code loading
	- the shell

   As well in the core.

   (But no snmp, mnesia, .... asn1 etc.) these are *applications* written in
Erlang - and no gen_server ... etc.)

  IMHO  gen_tcp  etc.  dets  should  be  written  so  they  don't  use
gen_severer etc.  - BTW my stand-alone Erlang broke just when I wanted
to use dets and gen_tcp - the reason was the dets and gen_tcp uses all
the application stuff and the gen_* stuff.

  One  of the  basic design  principles  underlying the  system is  (as
Martin Björkland said)

  "There is stuff  that has to be right, and stuff  that doesn't - you
have to make you mind up."

  IMHO the core should NOT be able to recover from errors - you get the core
right - period.

  Applications  outside the  core can  if they  wish build  upon gen_*
modules  to make the  apps. fault-tolerant  - but  the core  should be
A. Priori assumed correct - and have no such code.

  This is *why* the core should be as small as possible and include as
much pure code as possible (i.e code like in lists etc.)

  I think the discussion should proceed upon a module per. module basis.

  We should not be talking about which component lives in the core
(i.e. do we include snmp, corba etc.) but the discussion should be ...

  The core is compiler+stdlib+sasl+kernel with the following
changes:

  The following modules are *removed* 
	
	supervisor_bridge.erl
	sos.erl
	supervisor.erl
     	gen_*.erl
	...       etc.

  Then  all the  remaining modules  should  be re-written  so that  NO
references are made to the stuff that is removed.

  Finally we  will be able  to give an  exact and final list  of every
module in  the core with  a written argument that  motivates *exactly*
why it in the core.

  When this has been done I will be happy.

  IMHO the  average programmer should  be able to easily  remember all
the Erlang primitive and know about *all* the core modules do - Erlang
should and must be  a *small* langauge - that is easy  top learn - the
core libraries should have the same properties.

  I can  volunteer to do this (I  can't do Jocke's big  project) - but
I'd need help (i.e.  volunteers to *remove* non core-dependencies from
dets and gen_tcp etc.).

  All this  pre-supposes that the OTP  people like the idea  - since I
don't want to get into the "two systems" argument.

  For those  people who like the  "big and everything  release" we can
bundle the  core with  *all* the applications  - if that's  what turns
them on.

  I view  recoding and re-organizing the  core as *essential*  - in so
much as this will yield a tighter and more easily maintained system.

  Actually the  job is easier  than you imaging  - you first  throw out
*everything* you cannot explicitly motivate  - then run - xref - this
tells you  which modules  you have to  re-write. The modules  you have
removed you  move to a  set of libraries  outside the core,  and then
re-write them using stuff *inside* core.

  Comments?



	/Joe


> 
> It would be nice if the build process asked what you wanted to build.  It
> is a pain to be waiting for your shiny new emulator to arrive and see that
> it's wasting your time building Corba tools.  I've adopted the procedure
> of first touching lib/cosEvent/SKIP etc.
> 
> 	-Vance
>