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Hey, Erlang

Pre-alpha Kottans courses

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Advanced Erlang code structures

Lecture 4.

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Modules

Modules

Modules

  • Erlang module is a group of connected functions in common namespace

Modules

  • Erlang module is a group of connected functions in common namespace
  • can contain attributes

Modules

  • Erlang module is a group of connected functions in common namespace
  • can contain attributes
  • the only required attribute is module name (-module(Module))

Modules

  • Erlang module is a group of connected functions in common namespace
  • can contain attributes
  • the only required attribute is module name (-module(Module))
  • can export functions (-export(Functions))

Modules

  • Erlang module is a group of connected functions in common namespace
  • can contain attributes
  • the only required attribute is module name (-module(Module))
  • can export functions (-export(Functions))
  • can import functions (-import(Module, Functions))

Modules

  • Erlang module is a group of connected functions in common namespace
  • can contain attributes
  • the only required attribute is module name (-module(Module))
  • can export functions (-export(Functions))
  • can import functions (-import(Module, Functions))
  • can receive options for compiler (-compile(Options))

Modules

  • Erlang module is a group of connected functions in common namespace
  • can contain attributes
  • the only required attribute is module name (-module(Module))
  • can export functions (-export(Functions))
  • can import functions (-import(Module, Functions))
  • can receive options for compiler (-compile(Options))
  • can contain version (-vsn(Version))

Modules

  • Erlang module is a group of connected functions in common namespace
  • can contain attributes
  • the only required attribute is module name (-module(Module))
  • can export functions (-export(Functions))
  • can import functions (-import(Module, Functions))
  • can receive options for compiler (-compile(Options))
  • can contain version (-vsn(Version))
  • can execute function on loading (-on_load(Function))

Modules

Modules

In general modules can contain:

Modules

In general modules can contain:

  • function declarations

Modules

In general modules can contain:

  • function declarations
  • type declarations

Modules

In general modules can contain:

  • function declarations
  • type declarations
  • record declarations

Modules

In general modules can contain:

  • function declarations
  • type declarations
  • record declarations
  • macros

Modules

In general modules can contain:

  • function declarations
  • type declarations
  • record declarations
  • macros
  • another attributes

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Modules

Function declarations

Modules

Function declarations

Modules

Function declarations

  • is a sequence of function clauses separated by ;

Modules

Function declarations

  • is a sequence of function clauses separated by ;
  • consists of clause head and clause body, separated by ->

Modules

Function declarations

  • is a sequence of function clauses separated by ;
  • consists of clause head and clause body, separated by ->
  • head consists of name, argument list and optional guard

Modules

Function declarations

  • is a sequence of function clauses separated by ;
  • consists of clause head and clause body, separated by ->
  • head consists of name, argument list and optional guard
  • body consists of sequence of expressions separated by ,

Modules

Function declarations

  • is a sequence of function clauses separated by ;
  • consists of clause head and clause body, separated by ->
  • head consists of name, argument list and optional guard
  • body consists of sequence of expressions separated by ,
fact(N) when N>0 -> % first clause head (name atom, args list + guard)
  N * fact(N-1);    % first clause body
fact(0) ->          % second clause head
  1.                % second clause body and end of function

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Modules

Type declarations and specifications

Modules

Type declarations and specifications

Modules

Type declarations and specifications

Erlang allows developer to define user types. This definitions can be used internally for function specifications, externally (known as remote types) and in records.

Modules

Type declarations and specifications

Erlang allows developer to define user types. This definitions can be used internally for function specifications, externally (known as remote types) and in records.

  • has to be derived from predefined types

Modules

Type declarations and specifications

Erlang allows developer to define user types. This definitions can be used internally for function specifications, externally (known as remote types) and in records.

  • has to be derived from predefined types
  • has to have unique name if exported (inside module)

Modules

Type declarations and specifications

Erlang allows developer to define user types. This definitions can be used internally for function specifications, externally (known as remote types) and in records.

  • has to be derived from predefined types
  • has to have unique name if exported (inside module)
  • can be used for static type analyzer tool like Dialyzer or for documentation

Modules

Type declarations and specifications

Erlang allows developer to define user types. This definitions can be used internally for function specifications, externally (known as remote types) and in records.

  • has to be derived from predefined types
  • has to have unique name if exported (inside module)
  • can be used for static type analyzer tool like Dialyzer or for documentation
-module(mod).
-type orddict(Key, Val) :: [{Key, Val}]. % type with name orddict and args Key and Val
-export_type([orddict/2]). % list with types and their arity

% example of usage in record
-record(ordrec, {field1 :: orddict()}). % record can contain field1 which is orddict
% example of usage in specification
-spec fact(N :: integer()) -> integer(). % N argument of function fact can only be integer and result is integer too

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Modules

Record declarations

Modules

Record declarations

Modules

Record declarations

As you remember, record is syntax sugar for tuple with named fields.

-record(person, {name = "", phone = [], address}). % definition of record in module
-record(name, {first = "Robert", last = "Ericsson"}).
-record(person, {name = #name{}, phone}). % example of nested record

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Modules

Macros

Modules

Macros

Macro is an special instruction for compiler. They can be user-defined or predefined.

-define(Const, Replacement). % Const will be replaced in time of compiling with Replacement value
-define(TIMEOUT, 200). % example of above

-define(MACRO1(X, Y), {a, X, b, Y}). % example of parameters in macros

Modules

Macros

Macro is an special instruction for compiler. They can be user-defined or predefined.

  • ?MODULE - atom name of current module

Modules

Macros

Macro is an special instruction for compiler. They can be user-defined or predefined.

  • ?MODULE - atom name of current module
  • ?MODULE_STRING - string name of current module

Modules

Macros

Macro is an special instruction for compiler. They can be user-defined or predefined.

  • ?MODULE - atom name of current module
  • ?MODULE_STRING - string name of current module
  • ?FILE - file name of current module

Modules

Macros

Macro is an special instruction for compiler. They can be user-defined or predefined.

  • ?MODULE - atom name of current module
  • ?MODULE_STRING - string name of current module
  • ?FILE - file name of current module
  • ?LINE - current line number

Modules

Macros

Macro is an special instruction for compiler. They can be user-defined or predefined.

  • ?MODULE - atom name of current module
  • ?MODULE_STRING - string name of current module
  • ?FILE - file name of current module
  • ?LINE - current line number
  • ?MACHINE - virtual machine name, BEAM

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Expressions

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Expressions

Case

Expressions

Case

case Expr of
  Pattern1 [when GuardSeq1] ->
    Body1;
  ...;
  PatternN [when GuardSeqN] ->
    BodyN
end

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Expressions

If

Expressions

If

if
  GuardSeq1 ->
    Body1;
  ...;
  GuardSeqN ->
    BodyN;
  true -> % works as else branch
    Result
end

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Expressions

Try...catch...after

Expressions

Try...catch...after

try Exprs of
  Pattern1 [when GuardSeq1] ->
    Body1;
  ...;
  PatternN [when GuardSeqN] ->
    BodyN
catch
  [Class1:]ExceptionPattern1 [when ExceptionGuardSeq1] ->
    ExceptionBody1;
  ...;
  [ClassN:]ExceptionPatternN [when ExceptionGuardSeqN] ->
    ExceptionBodyN
after
  AfterBody
end

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Expressions

Receive

Expressions

Receive

receive
  Pattern1 [when GuardSeq1] ->
    Body1;
  ...;
  PatternN [when GuardSeqN] ->
    BodyN
after
  ExprT -> % ExprT :: integer(), timeout for receive loop
    BodyT
end

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Comparison

Comparison

  • == - equal to

Comparison

  • == - equal to
  • /= - not equal to

Comparison

  • == - equal to
  • /= - not equal to
  • =< - less than

Comparison

  • == - equal to
  • /= - not equal to
  • =< - less than or equal to
  • < - less than

Comparison

  • == - equal to
  • /= - not equal to
  • =< - less than or equal to
  • < - less than
  • >= - greater than or equal to

Comparison

  • == - equal to
  • /= - not equal to
  • =< - less than or equal to
  • < - less than
  • >= - greater than or equal to
  • > - greater than

Comparison

  • == - equal to
  • /= - not equal to
  • =< - less than or equal to
  • < - less than
  • >= - greater than or equal to
  • > - greater than
  • =:= - exactly equal to

Comparison

  • == - equal to
  • /= - not equal to
  • =< - less than or equal to
  • < - less than
  • >= - greater than or equal to
  • > - greater than
  • =:= - exactly equal to
  • =/= - exactly not equal to

Comparison

  • == - equal to
  • /= - not equal to
  • =< - less than or equal to
  • < - less than
  • >= - greater than or equal to
  • > - greater than
  • =:= - exactly equal to
  • =/= - exactly not equal to
  • types comparison order: number < atom < reference < fun < port < pid < tuple < list < bit string

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End of Lecture 4

Subject of next lecture: Concurrency, scaling, multiprocessing.

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Bye, folks!

Joe with notebook