Tag: elixir

Elixir iex documentation : C

~ chriseyre2000 ~ Leave a comment

This is the third part of an exploration of the Elixir base libraries

Here is an introduction to what you get out of the box with iex:

LetterModuleDescription
CCalendarDate, time and calendar functions
CaseClauseErrorThis is a struct used for errors.
CodeUtilities for managing code compilation, code
evaluation, and code loading.
CollectableProtocol to traverse data structures.
Used for putting data into things.
CompileErrorThis is a struct used for errors.
CondClauseErrorThis is a struct used for errors.

Doing the same with :c gives the erlang modules

LetterModuleDescription
ccErlang compiler.
calendarDate, time and calendar functions
cerlCore Erlang abstract syntax trees.
cerl_clausesUtility functions for Core Erlang
case/receive clauses.
cerl_inline???
cerl_setsSet functions.
cerl_treesBasic functions on Core Erlang abstract syntax trees.
codeUtilities for managing code compilation, code
evaluation, and code loading.
code_serverProcess used for live code reloading
compileErlang compiler interface
core_lib???
core_lint
core_parse
core_pp
core_scan
countersLibrary of mutable counters with no locking.

Elixir iex documentation : B

~ chriseyre2000 ~ Leave a comment

This is the second part of an exploration of the Elixir base libraries

Here is an introduction to what you get out of the box with iex:

LetterModuleDescription
BBadArityErrorThis is a struct used for errors.
BadBooleanErrorThis is a struct used for errors.
BadFunctionErrorThis is a struct used for errors.
BadMapErrorThis is a struct used for errors.
BadStructErrorThis is a struct used for errors.
BaseEncoding and decoding functions
for 16, 32, 64, hex, url
BehaviourMechanism for handling behaviours
(deprecated)
BitwisePerforms bit calculations.

Doing the same with :b gives the erlang modules

LetterModuleDescription
bbase64Base 64 encode and decode
beam_aUsed after code generation before
optimisation. Normalises the code.
beam_asmAssembler for the beam
beam_blockErlang compiler
beam_bsErlang compiler
beam_bsmErlang compiler
beam_cleanErlang compiler
beam_deadErlang compiler
beam_dictErlang compiler
beam_disamErlang compiler
beam_exceptErlang compiler
beam_flattenErlang compiler
beam_jumpErlang compiler
beam_libErlang compiler
beam_listingErlang compiler
beam_opcodesErlang compiler
beam_peepErlang compiler
beam_receiveErlang compiler
beam_recordErlang compiler
beam_reorderErlang compiler
beam_splitErlang compiler
beam_trimErlang compiler
beam_typeErlang compiler
beam_utilsErlang compiler
beam_validatorErlang compiler
beam_zErlang compiler
binaryHandles binary data.
This is the Erlang string type

Elixir iex documentation : A

~ chriseyre2000 ~ Leave a comment

I recently found out how powerful the iex tool is for documentation.

This is the general form of getting detailed documentation:

This is the start of a long series about the modules that you get out of the box.
1> h Module.function_name/arity

This returns the documentation on this specific function in the specific module.

I also found that typing a capital letter and tab expands the known modules.

Here is an introduction to what you get out of the box with iex:

LetterModuleDescription
AAccessKey based access to structures.
AgentSimple abstraction around state
ApplicationWorking with applications and their callbacks
ArgumentErrorThis is a struct used for errors.
ArithmeticError This is a struct used for errors.
AtomConvenience functions for working with atoms.

Translating Elixir/Erlang terms:

An application is equivalent of a windows DLL, something that you compose a system out of. A typical application would be a logging system.

Atoms are a non-garbage collected resource. They make convenient aliases to global things.

Doing the same with :a gives the erlang modules

LetterModuleDescription
aapplicationGeneric OTP Application
application_controllerKernel supplied application controller
application_masterKernel supplied application master.
Responsible for knowing the topmost
supervisor
application_starterResponsible for starting applications in
a defined order
arrayArray structure, fixed or extensible
atomicsProvides atomic operations using
hardware instructions
authErlang network authentication server
(deprecated)

Designing Elixir Systems With OTP – Part Two

~ chriseyre2000 ~ Leave a comment

I have continued working through this beta book and have updated the github repo: github.com/chriseyre2000/designing_elixir with the samples.

So far this book is easier to follow than say Programming Phoenix since it does not keep changing the code that you are working on. The testing code is normally close to where you have typed it, so finding mistakes does not require too much effort. I would recommend using mix test after each code sample has been typed in as fixing errors can be tricky.

Note the only difference between my code and the supplied sample is the use of the british name Maths rather than Math for the sample code. My degree is in Mathematics so I can’t let a typo like that stand!

The main points from the second half of the book are the very clean validation techniques used. I like that they called the process returned by start_link a session.

The book currently stops at the end of chapter 6, so I will have to resume work on this series once it has been updated.

Tools to help Elixir Exercism.IO Mentors

~ chriseyre2000 ~ Leave a comment

I have been mentoring Elixir on Exercism.IO for about 6 months.

Over that time I have started to build a collection of tools to help with the mentoring.

This is the major trick that I use to help find problems:

grep -v @tag *_test.exs > test.exs && elixir test.

I also have my notes for mentoring:

https://devrants.blog/useful-elixir-links/

I have now found that you can install credo to run globally (apparently this is contentious – it can cause problems if you have different versions installed locally and globally):

git clone git@github.com:rrrene/bunt.git

cd bunt

mix archive.build

mix archive.install

cd –

git clone git@github.com:rrrene/credo.git

cd credo

mix deps.get

mix archive.build

mix archive.install

Once you have that then you can now use:

mix credo *.exs –verbose –strict

It’s also useful if students are having trouble with documentation to submit pull requests to:

  • elixirschool.com – Elixir training
  • elixir-lang – Elixir documentation
  • elixir – Hex docs

Getting Started With Phoenix 1.4 (Part 3)

~ chriseyre2000 ~ Leave a comment

Continuing the way through the book.

Now have reached the end of Chapter 6.

This adds video to use associations. It includes some of the clever techniques that Phoenix uses to allow the templates to be customised.

By adding an action method you can customise the parameters passed to the various utility methods:

def action(conn, _) do args = [conn, conn.params, conn.assigns.current_user] apply(__MODULE__, action_name(conn), args) end

This allows details from the conn to be decomposed and passed as a parameter.

https://github.com/chriseyre2000/rumbl_1_4

Elixir Supervisor Introduction

~ chriseyre2000 ~ Leave a comment

This is a simple introduction to OTP in Elixir.

The sample is based heavily upon Introducing Elixir.

This will demonstrate how Elixir keeps a server alive across code recompilation, and restores a server after it has crashed.

This assumes that you have installed Elixir.

On a mac you can install this with (there are other solutions on other platforms):

brew install elixir

Start by cloning the repo:

git clone https://github.com/chriseyre2000/drop_server.git

Change directory into the drop_server folder.

Type

iex -S mix

This will start the application running inside the interactive Elixir REPL.

This application has a DropServer.Worker being monitored by a supervisor.

First you can calculate the velocity after falling a distance in meters:

(Type the bit after the iex> prompts):

iex(1)> DropServer.Worker.calculate_drop(40)

{“ok”, 28.0}

iex(2)> DropServer.Worker.calculate_drop(41)

{“ok”, 28.347839423843222}

iex(3)> DropServer.Worker.calculate_drop(42)

{“ok”, 28.691462144686877}

iex(4)> DropServer.Worker.how_many_calls

So far calculated 3 velocities.

:ok

You can even recompile the DropServer.Worker while it is running:

iex(5)> c(“lib/drop_server/drop_server.ex”)

warning: redefining module DropServer.Worker (current version loaded from _build/dev/lib/drop_server/ebin/Elixir.DropServer.Worker.beam)

lib/drop_server/drop_server.ex:1

warning: redefining module DropServer.Worker.State (current version loaded from _build/dev/lib/drop_server/ebin/Elixir.DropServer.Worker.State.beam)

lib/drop_server/drop_server.ex:4

[DropServer.Worker, DropServer.Worker.State]

This even maintains the state:

iex(6)> DropServer.Worker.how_many_calls

So far calculated 3 velocities.

:ok

Now if you give it some invalid data Elixir will do the classic Erlang thing and let it crash!

iex(7)> DropServer.Worker.calculate_drop(-1)

21:49:21.278 [error] GenServer DropServer.Worker terminating

** (ArithmeticError) bad argument in arithmetic expression

(stdlib) :math.sqrt(-19.6)

(drop_server) lib/drop_server/drop_server.ex:44: DropServer.Worker.fall_velocity/1

(drop_server) lib/drop_server/drop_server.ex:20: DropServer.Worker.handle_call/3

(stdlib) gen_server.erl:661: :gen_server.try_handle_call/4

(stdlib) gen_server.erl:690: :gen_server.handle_msg/6

(stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3

Last message (from #PID<0.133.0>): -1

State: %DropServer.Worker.State{count: 3}

Client #PID<0.133.0> is alive

(stdlib) gen.erl:169: :gen.do_call/4

(elixir) lib/gen_server.ex:921: GenServer.call/3

(stdlib) erl_eval.erl:680: :erl_eval.do_apply/6

(elixir) src/elixir.erl:265: :elixir.eval_forms/4

(iex) lib/iex/evaluator.ex:249: IEx.Evaluator.handle_eval/5

(iex) lib/iex/evaluator.ex:229: IEx.Evaluator.do_eval/3

(iex) lib/iex/evaluator.ex:207: IEx.Evaluator.eval/3

(iex) lib/iex/evaluator.ex:94: IEx.Evaluator.loop/1

** (exit) exited in: GenServer.call(DropServer.Worker, -1, 5000)

** (EXIT) an exception was raised:

** (ArithmeticError) bad argument in arithmetic expression

(stdlib) :math.sqrt(-19.6)

(drop_server) lib/drop_server/drop_server.ex:44: DropServer.Worker.fall_velocity/1

(drop_server) lib/drop_server/drop_server.ex:20: DropServer.Worker.handle_call/3

(stdlib) gen_server.erl:661: :gen_server.try_handle_call/4

(stdlib) gen_server.erl:690: :gen_server.handle_msg/6

(stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3

(elixir) lib/gen_server.ex:924: GenServer.call/3

However only the state is lost:

iex(7)> DropServer.Worker.how_many_calls

So far calculated 0 velocities.

:ok

iex(8)> DropServer.Worker.calculate_drop(10)

{“ok”, 14.0}

iex(9)> DropServer.Worker.how_many_calls

So far calculated 1 velocities.

:ok

The supervisor has restarted the server.

In a real service the state would have been kept in a distinct service possibly with some form of persistence.

Elixir Metaprogramming : the basics

~ chriseyre2000 ~ Leave a comment

Elixir has a very small core language. Most of what is thought of as the syntax is actually written using macros.

Elixir makes it ridiculously easy to get at the Abstract Syntax Tree (AST) of the code that you are using.

How to get the AST of some code:

iex(1)> quote do: 1 + 1
{:+, [context: Elixir, import: Kernel], [1, 1]}

Httpoison on windows

~ chriseyre2000 ~ Leave a comment

I have been having trouble getting the Httpoison library working on my windows development machine. I had put this down to portability issues in the past.

Last weekend I spent some time trying to track down the bug so that I could send a patch to the appropriate project.

During this investigation I found that I had been using a fairly old version of Erlang (10) which seemed to work everywhere else but had a problem with the crypto checking that HTTPoison performs. I had installed Erlang when studying 7 languages in 7 weeks over 6 years ago.

Moral of the story: don’t blame the tools, try to fix them and you may find the source of the problem.