Industrial use of a functional language
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Thomas Arts. Industrial Use of a Functional Language. Thomas Arts Ericsson Computer Science Laboratory Stockholm, Sweden. [email protected] http://www.ericsson.se/cslab/~thomas. Thomas Arts. Telecom industry. Switches, routers, base-stations Networks Mobile telephones.

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Industrial Use of a Functional Language

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Thomas Arts

Industrial Use of a Functional Language

Thomas Arts

Ericsson

Computer Science Laboratory

Stockholm, Sweden

[email protected]

http://www.ericsson.se/cslab/~thomas


Thomas Arts

Telecom industry

Switches, routers,

base-stations

Networks

Mobile telephones


Thomas Arts

Computer ScienceLaboratory

Founded 1983

Research on implementation tools, methods and techniques for telecommunication applications

Intermediate between universities and Ericsson product units


Thomas Arts

Telecom requirements

Requirements of telecom software

Concurrency

Distribution

Soft real-time

Robust

Non-stop system

External interfaces


Thomas Arts

A good language?

Experiments in the 80s with Ada, C, ML, CML, Prolog...

large programs (million lines)

change code in running system

fast message passing

low memory overhead

no memory fragmentation/leaks

recover from errors


Thomas Arts

Erlang/OTP

A functional language successfully used for programming large real-time control systems.

OTP is the set of libraries that is used with Erlang for product development


Thomas Arts

Erlang/OTP

Erlang/OTP develop/maintenance

Erlang consultancy & courses

Erlang used many systems, e.g. ATM switch and new GSM network (GPRS)

Erlang Open Source

www.erlang.org


Thomas Arts

Erlangsequential program

-module(math).

-export([fac/1]).

fac(N) when N>0 ->

N*fac(N-1);

fac(N)->

1.


Thomas Arts

Erlangdatatypes

atoms (true,foo,’Hello’)

numbers (1212864187154)

floats (3.141592)

tuples ({a,123})

lists ([1,123,2,56])

process identifiers

...


Thomas Arts

Erlangdatatypes

dynamically typed language

poor mechanism to build your own datatypes


Thomas Arts

Erlangcontrol structures

Matching

case X of

{ok,List} -> hd(List);

{resend,Data} -> submit;

error -> exit(error);

_ -> retry(X)

end


Thomas Arts

Erlangcontrol structures

Guards

f(....) when guard -> ...

If

f(X) ->

if guard1 -> ...;

guard2 -> ...

end


Thomas Arts

Erlangcontrol structures

Higher order functions

f(F,X) -> F(X);

map(F,[1,2,3,4]).

List comprehensions

[ X || {X,Y}<-Set, guard(X)]


Thomas Arts

Erlangcontrol structures

Naming of objects/data

f(X) ->

Dev = update_device(X),

{Date,Time} = now(),

h({Dev,Date}).


Thomas Arts

Erlangcontrol structures

Sequence

f(X) ->

action1(X),

action2(X);

update(X) ->

log(X,”myfile”), new(X).

side-effects


Thomas Arts

Erlangcontrol - concurrency/distribution

Creating a process

Pid = spawn(F,[Arg1,...,ArgN]);

B = spawn(F,Args);

P2

P1

P2

F(Arg1,...,ArgN)


{P1,hej}

Thomas Arts

Erlangcontrol - concurrency/distribution

Sending messages

Pid ! Message;

B!{self(),hej};

P1

P2

{P1,hej}


Thomas Arts

Erlangcontrol - concurrency/distribution

Receiving messages

receive

Pattern -> ...;

end;

P1

P2

{P1,hej}

receive

{From,Msg} ->

From ! {ok,Msg}

end

P1 ! {ok,hej}


Thomas Arts

Erlangchanging code in running system

P0

loop(F) ->

receive

{change,G} ->

loop(G);

{exec,Pid,Arg} ->

Pid!F(Arg),

loop(F)

end;

loop(F) ->

receive

{exec,Pid,Arg} ->

Pid!F(Arg),

loop(F)

end;

P1

P0 ! {exec,self(),15},

N = receive

Answer ->

Answer

end,

N = F(15),


Thomas Arts

Erlangfault tolerance

Processes can be linked to each other:

PidA

PidB

  • Links are created by using either:

  • link(Pid), or

  • spawn_link(Module, Function, Args)

  • Links are bi-directional.

  • They can be removed using unlink(Pid).


Thomas Arts

Erlangfault tolerance

When a process terminates, an exit signal is sent to all processes the process is linked to:

PidA

PidA

PidB

A process can terminate normally, due to a run-time error, or when explicitly ordered to do so.


Thomas Arts

Erlangfault tolerance

If a process terminates abnormally, the emitted exit signal will (by default) cause the recipient to terminate:

The termination reason in the transmitted exit signals will be the same as in the received one (the exit signal is propagated).

PidA

PidB

PidB

PidC

PidD

PidD

PidE


error

error

PidA

PidB

PidC

exit(error)

Thomas Arts

Erlangfault tolerance

A process can terminate itself using exit(Reason). This will cause exit signals with termination reason Reason to be emitted.


error

PidA

PidB

exit(PidB, error)

Thomas Arts

Erlangfault tolerance

A process can explicitly send an exit signal to another process using exit(Pid, Reason):

  • The calling process is not affected.

  • The processes do not need to be linked.


Thomas Arts

Erlangfault tolerance

A process can trap exit signals using:

process_flag(trap_exit, true).

Incoming exit signals will be transformed into messages of the form: {'EXIT', Pid, Reason}

These exit messages are delivered to the process mailbox in the normal way.


Thomas Arts

Erlangfault tolerance

PidC terminates with reason error, PidD is trapping exits:

PidB terminates, propagating the exit signal. PidD will receive an exit message

{'EXIT', PidC, error}.

error

error

PidA

PidA

PidB

PidB

PidC

PidD

PidE


Thomas Arts

Erlangfault tolerance

Robust systems can be made by layering.


Thomas Arts

Erlangfault tolerance

supervision trees and restart strategies

P4

P3

P1

P2

P3

P1

P5

P6

P4

P2

P3

P1


Thomas Arts

Erlangcomponent based development

  • recognize frequently occurring

  • patterns and transfer them into

  • standard components.

  • faster development

  • uniform code (maintenance)

  • less errors


Thomas Arts

Erlang

Developed with the application of the language constantly in mind

Practical usability more priority than purity


Thomas Arts

Erlang is used

AXD 301, scalable ATM switch (up to 160 GB/sec)

  • four years work

  • more than 500,000 lines of Erlang

  • several hundreds of programmers


Thomas Arts

Erlang is used

GPRS: next generation GSM network.

  • Eigth times faster internet access in mobile phones

  • always connected

  • development in three countries, hundreds of people


Thomas Arts

Erlang is used

The success of the language in industry is due to

Language features

Support and libraries

Design patterns / architectures


Thomas Arts

over

300 downloads

per month

Erlang is used

Become a user yourself!

passive: make a phonecall

active: download Erlang for free

www.erlang.org


Thomas Arts

Erlang

The functional language

for industry


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