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-rwxr-xr-xsystem/doc/reference_manual/typespec.xml615
1 files changed, 324 insertions, 291 deletions
diff --git a/system/doc/reference_manual/typespec.xml b/system/doc/reference_manual/typespec.xml
index 52dc0c943e..981a44642a 100755
--- a/system/doc/reference_manual/typespec.xml
+++ b/system/doc/reference_manual/typespec.xml
@@ -4,7 +4,7 @@
<chapter>
<header>
<copyright>
- <year>2003</year><year>2009</year>
+ <year>2003</year><year>2010</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
@@ -139,326 +139,359 @@ Tuple :: tuple() %% stands for a tuple of any size
TList :: Type
| Type, TList
]]></pre>
- <p>
- Because lists are commonly used, they have shorthand type notations.
- The type <c>list(T)</c> has the shorthand <c>[T]</c>. The shorthand <c>[T,...]</c> stands for
- the set of non-empty proper lists whose elements are of type <c>T</c>.
- The only difference between the two shorthands is that <c>[T]</c> may be an
- empty list but <c>[T,...]</c> may not.
- </p>
- <p>
- Notice that the shorthand for <c>list()</c>, i.e. the list of elements of unknown type,
- is <c>[_]</c> (or <c>[any()]</c>), not <c>[]</c>.
- The notation <c>[]</c> specifies the singleton type for the empty list.
- </p>
- <p>
- For convenience, the following types are also built-in.
- They can be thought as predefined aliases for the type unions also shown in
- the table. (Some type unions below slightly abuse the syntax of types.)
- </p>
- <table>
- <row>
- <cell><b>Built-in type</b></cell><cell><b>Stands for</b></cell>
- </row>
- <row>
- <cell><c>term()</c></cell><cell><c>any()</c></cell>
- </row>
- <row>
- <cell><c>bool()</c></cell><cell><c>'false' | 'true'</c></cell>
- </row>
- <row>
- <cell><c>byte()</c></cell><cell><c>0..255</c></cell>
- </row>
- <row>
- <cell><c>char()</c></cell><cell><c>0..16#10ffff</c></cell>
- </row>
- <row>
- <cell><c>non_neg_integer()</c></cell><cell><c>0..</c></cell>
- </row>
- <row>
- <cell><c>pos_integer()</c></cell><cell><c>1..</c></cell>
- </row>
- <row>
- <cell><c>neg_integer()</c></cell><cell><c>..-1</c></cell>
- </row>
- <row>
- <cell><c>number()</c></cell><cell><c>integer() | float()</c></cell>
- </row>
- <row>
- <cell><c>list()</c></cell><cell><c>[any()]</c></cell>
- </row>
- <row>
- <cell><c>maybe_improper_list()</c></cell><cell><c>maybe_improper_list(any(), any())</c></cell>
- </row>
- <row>
- <cell><c>maybe_improper_list(T)</c></cell><cell><c>maybe_improper_list(T, any())</c></cell>
- </row>
- <row>
- <cell><c>string()</c></cell><cell><c>[char()]</c></cell>
- </row>
- <row>
- <cell><c>nonempty_string()</c></cell><cell><c>[char(),...]</c></cell>
- </row>
- <row>
- <cell><c>iolist()</c></cell><cell><c>maybe_improper_list(
-char() | binary() | iolist(), binary() | [])</c></cell>
- </row>
- <row>
- <cell><c>module()</c></cell><cell><c>atom()</c></cell>
- </row>
- <row>
- <cell><c>mfa()</c></cell><cell><c>{atom(),atom(),byte()}</c></cell>
- </row>
- <row>
- <cell><c>node()</c></cell><cell><c>atom()</c></cell>
- </row>
- <row>
- <cell><c>timeout()</c></cell><cell><c>'infinity' | non_neg_integer()</c></cell>
- </row>
- <row>
- <cell><c>no_return()</c></cell><cell><c>none()</c></cell>
- </row>
- </table>
-
- <p>
- Users are not allowed to define types with the same names as the predefined or
- built-in ones.
- This is checked by the compiler and its violation results in a compilation
- error.
- (For bootstrapping purposes, it can also result to just a warning if this
- involves a built-in type which has just been introduced.)
- </p>
- <note>
- The following built-in list types also exist,
- but they are expected to be rarely used. Hence, they have long names:
- </note>
- <pre>
+ <p>
+ Because lists are commonly used, they have shorthand type notations.
+ The type <c>list(T)</c> has the shorthand <c>[T]</c>.
+ The shorthand <c>[T,...]</c> stands for
+ the set of non-empty proper lists whose elements are of type <c>T</c>.
+ The only difference between the two shorthands is that <c>[T]</c> may be an
+ empty list but <c>[T,...]</c> may not.
+ </p>
+ <p>
+ Notice that the shorthand for <c>list()</c>, i.e. the list of
+ elements of unknown type, is <c>[_]</c> (or <c>[any()]</c>), not <c>[]</c>.
+ The notation <c>[]</c> specifies the singleton type for the empty list.
+ </p>
+ <p>
+ For convenience, the following types are also built-in.
+ They can be thought as predefined aliases for the type unions also shown in
+ the table. (Some type unions below slightly abuse the syntax of types.)
+ </p>
+ <table>
+ <row>
+ <cell><b>Built-in type</b></cell><cell><b>Stands for</b></cell>
+ </row>
+ <row>
+ <cell><c>term()</c></cell><cell><c>any()</c></cell>
+ </row>
+ <row>
+ <cell><c>bool()</c></cell><cell><c>'false' | 'true'</c></cell>
+ </row>
+ <row>
+ <cell><c>byte()</c></cell><cell><c>0..255</c></cell>
+ </row>
+ <row>
+ <cell><c>char()</c></cell><cell><c>0..16#10ffff</c></cell>
+ </row>
+ <row>
+ <cell><c>non_neg_integer()</c></cell><cell><c>0..</c></cell>
+ </row>
+ <row>
+ <cell><c>pos_integer()</c></cell><cell><c>1..</c></cell>
+ </row>
+ <row>
+ <cell><c>neg_integer()</c></cell><cell><c>..-1</c></cell>
+ </row>
+ <row>
+ <cell><c>number()</c></cell><cell><c>integer() | float()</c></cell>
+ </row>
+ <row>
+ <cell><c>list()</c></cell><cell><c>[any()]</c></cell>
+ </row>
+ <row>
+ <cell><c>maybe_improper_list()</c></cell><cell><c>maybe_improper_list(any(), any())</c></cell>
+ </row>
+ <row>
+ <cell><c>maybe_improper_list(T)</c></cell><cell><c>maybe_improper_list(T, any())</c></cell>
+ </row>
+ <row>
+ <cell><c>string()</c></cell><cell><c>[char()]</c></cell>
+ </row>
+ <row>
+ <cell><c>nonempty_string()</c></cell><cell><c>[char(),...]</c></cell>
+ </row>
+ <row>
+ <cell><c>iolist()</c></cell><cell><c>maybe_improper_list(char() | binary() | iolist(), binary() | [])</c></cell>
+ </row>
+ <row>
+ <cell><c>module()</c></cell><cell><c>atom()</c></cell>
+ </row>
+ <row>
+ <cell><c>mfa()</c></cell><cell><c>{atom(),atom(),byte()}</c></cell>
+ </row>
+ <row>
+ <cell><c>node()</c></cell><cell><c>atom()</c></cell>
+ </row>
+ <row>
+ <cell><c>timeout()</c></cell><cell><c>'infinity' | non_neg_integer()</c></cell>
+ </row>
+ <row>
+ <cell><c>no_return()</c></cell><cell><c>none()</c></cell>
+ </row>
+ </table>
+
+ <p>
+ Users are not allowed to define types with the same names as the
+ predefined or built-in ones. This is checked by the compiler and
+ its violation results in a compilation error.
+ (For bootstrapping purposes, it can also result to just a warning if this
+ involves a built-in type which has just been introduced.)
+ </p>
+ <note>
+ The following built-in list types also exist,
+ but they are expected to be rarely used. Hence, they have long names:
+ </note>
+ <pre>
nonempty_maybe_improper_list(Type) :: nonempty_maybe_improper_list(Type, any())
nonempty_maybe_improper_list() :: nonempty_maybe_improper_list(any())
- </pre>
- <p>
- where the following two types
- define the set of Erlang terms one would expect:
- </p>
- <pre>
+ </pre>
+ <p>
+ where the following two types
+ define the set of Erlang terms one would expect:
+ </p>
+ <pre>
nonempty_improper_list(Type1, Type2)
nonempty_maybe_improper_list(Type1, Type2)
- </pre>
- <p>
- Also for convenience, we allow for record notation to be used.
- Records are just shorthands for the corresponding tuples.
- </p>
- <pre>
+ </pre>
+ <p>
+ Also for convenience, we allow for record notation to be used.
+ Records are just shorthands for the corresponding tuples.
+ </p>
+ <pre>
Record :: #Erlang_Atom{}
| #Erlang_Atom{Fields}
+ </pre>
+ <p>
+ Records have been extended to possibly contain type information.
+ This is described in the sub-section <seealso marker="#typeinrecords">"Type information in record declarations"</seealso> below.
+ </p>
+ </section>
+
+ <section>
+ <title>Type declarations of user-defined types</title>
+ <p>
+ As seen, the basic syntax of a type is an atom followed by closed
+ parentheses. New types are declared using '-type' and '-opaque'
+ compiler attributes as in the following:
+ </p>
+ <pre>
+-type my_struct_type() :: Type.
+-opaque my_opaq_type() :: Type.
</pre>
<p>
- Records have been extended to possibly contain type information.
- This is described in the sub-section <seealso marker="#typeinrecords">"Type information in record declarations"</seealso> below.
- </p>
- </section>
-
- <section>
- <title>Type declarations of user-defined types</title>
- <p>
- As seen, the basic syntax of a type is an atom followed by closed
- parentheses. New types are declared using '-type' compiler attributes
- as in the following:
- </p>
- <pre>
--type my_type() :: Type.
- </pre>
- <p>
- where the type name is an atom (<c>'my_type'</c> in the above) followed by
- parenthesis. Type is a type as defined in the previous section.
- A current restriction is that Type can contain only predefined types
- or user-defined types which have been previously defined.
- This restriction is enforced by the compiler and results in a
- compilation error. (A similar restriction currently exists for records).
- </p>
- <p>
- This means that currently general recursive types cannot be defined.
- Lifting this restriction is future work.
- </p>
- <p>
- Type declarations can also be parameterized by including type variables
- between the parentheses. The syntax of type variables is the same as
- Erlang variables (starts with an upper case letter).
- Naturally, these variables can - and should - appear on the RHS of the
- definition. A concrete example appears below:
- </p>
- <pre>
+ where the type name is an atom (<c>'my_struct_type'</c> in the above)
+ followed by parentheses. Type is a type as defined in the
+ previous section.
+ A current restriction is that Type can contain only predefined types,
+ or user-defined types which are either module-local (i.e., with a
+ definition that is present in the code of the module) or are remote
+ types (i.e., types defined in and exported by other modules; see below).
+ For module-local types, the restriction that their definition
+ exists in the module is enforced by the compiler and results in a
+ compilation error. (A similar restriction currently exists for records.)
+ </p>
+ <p>
+ Type declarations can also be parameterized by including type variables
+ between the parentheses. The syntax of type variables is the same as
+ Erlang variables (starts with an upper case letter).
+ Naturally, these variables can - and should - appear on the RHS of the
+ definition. A concrete example appears below:
+ </p>
+ <pre>
-type orddict(Key, Val) :: [{Key, Val}].
- </pre>
-
- </section>
-
- <marker id="typeinrecords"/>
- <section>
- <title>
- Type information in record declarations
- </title>
- <p>
- The types of record fields can be specified in the declaration of the
- record. The syntax for this is:
- </p>
- <pre>
+ </pre>
+ <p>
+ A module can export some types in order to declare that other modules
+ are allowed to refer to them as <em>remote types</em>.
+ This declaration has the following form:
+ <pre>
+-export_type([T1/A1, ..., Tk/Ak]).
+ </pre>
+ where the Ti's are atoms (the name of the type) and the Ai's are their
+ arguments. An example is given below:
+ <pre>
+-export_type([my_struct_type/0, orddict/2]).
+ </pre>
+ Assuming that these types are exported from module <c>'mod'</c> then
+ one can refer to them from other modules using remote type expressions
+ like those below:
+ <pre>
+mod:my_struct_type()
+mod:orddict(atom(), term())
+ </pre>
+ One is not allowed to refer to types which are not declared as exported.
+ </p>
+ <p>
+ Types declared as <c>opaque</c> represent sets of terms whose
+ structure is not supposed to be visible in any way outside of
+ their defining module (i.e., only the module defining them is
+ allowed to depend on their term structure). Consequently, such
+ types do not make much sense as module local - module local
+ types are anyway not accessible by other modules - and should
+ always be exported.
+ </p>
+ </section>
+
+ <marker id="typeinrecords"/>
+ <section>
+ <title>
+ Type information in record declarations
+ </title>
+ <p>
+ The types of record fields can be specified in the declaration of the
+ record. The syntax for this is:
+ </p>
+ <pre>
-record(rec, {field1 :: Type1, field2, field3 :: Type3}).
- </pre>
- <p>
- For fields without type annotations, their type defaults to any().
- I.e., the above is a shorthand for:
- </p>
- <pre>
+ </pre>
+ <p>
+ For fields without type annotations, their type defaults to any().
+ I.e., the above is a shorthand for:
+ </p>
+ <pre>
-record(rec, {field1 :: Type1, field2 :: any(), field3 :: Type3}).
- </pre>
- <p>
- In the presence of initial values for fields,
- the type must be declared after the initialization as in the following:
- </p>
- <pre>
+ </pre>
+ <p>
+ In the presence of initial values for fields,
+ the type must be declared after the initialization as in the following:
+ </p>
+ <pre>
-record(rec, {field1 = [] :: Type1, field2, field3 = 42 :: Type3}).
- </pre>
- <p>
- Naturally, the initial values for fields should be compatible
- with (i.e. a member of) the corresponding types.
- This is checked by the compiler and results in a compilation error
- if a violation is detected. For fields without initial values,
- the singleton type <c>'undefined'</c> is added to all declared types.
- In other words, the following two record declarations have identical
- effects:
- </p>
- <pre>
+ </pre>
+ <p>
+ Naturally, the initial values for fields should be compatible
+ with (i.e. a member of) the corresponding types.
+ This is checked by the compiler and results in a compilation error
+ if a violation is detected. For fields without initial values,
+ the singleton type <c>'undefined'</c> is added to all declared types.
+ In other words, the following two record declarations have identical
+ effects:
+ </p>
+ <pre>
-record(rec, {f1 = 42 :: integer(),
f2 :: float(),
- f3 :: 'a' | 'b').
+ f3 :: 'a' | 'b'}).
-record(rec, {f1 = 42 :: integer(),
f2 :: 'undefined' | float(),
- f3 :: 'undefined' | 'a' | 'b').
- </pre>
- <p>
- For this reason, it is recommended that records contain initializers,
- whenever possible.
- </p>
- <p>
- Any record, containing type information or not, once defined,
- can be used as a type using the syntax:
- </p>
- <pre>
+ f3 :: 'undefined' | 'a' | 'b'}).
+ </pre>
+ <p>
+ For this reason, it is recommended that records contain initializers,
+ whenever possible.
+ </p>
+ <p>
+ Any record, containing type information or not, once defined,
+ can be used as a type using the syntax:
+ </p>
+ <pre>
#rec{}
- </pre>
- <p>
- In addition, the record fields can be further specified when using
- a record type by adding type information about the field in the following
- manner:
- </p>
- <pre>
+ </pre>
+ <p>
+ In addition, the record fields can be further specified when using
+ a record type by adding type information about the field in
+ the following manner:
+ </p>
+ <pre>
#rec{some_field :: Type}
- </pre>
- <p>
- Any unspecified fields are assumed to have the type in the original
- record declaration.
- </p>
- </section>
+ </pre>
+ <p>
+ Any unspecified fields are assumed to have the type in the original
+ record declaration.
+ </p>
+ </section>
- <section>
- <title>Specifications (contracts) for functions</title>
- <p>
- A contract (or specification) for a function is given using the new
- compiler attribute <c>'-spec'</c>. The basic format is as follows:
- </p>
- <pre>
+ <section>
+ <title>Specifications for functions</title>
+ <p>
+ A specification (or contract) for a function is given using the new
+ compiler attribute <c>'-spec'</c>. The general format is as follows:
+ </p>
+ <pre>
-spec Module:Function(ArgType1, ..., ArgTypeN) -> ReturnType.
- </pre>
- <p>
- The arity of the function has to match the number of arguments,
- or else a compilation error occurs.
- </p>
- <p>
- This form can also be used in header files (.hrl) to declare type
- information for exported functions.
- Then these header files can be included in files that (implicitly or
- explicitly) import these functions.
- </p>
- <p>
- For most uses within a given module, the following shorthand is allowed:
- </p>
- <pre>
+ </pre>
+ <p>
+ The arity of the function has to match the number of arguments,
+ or else a compilation error occurs.
+ </p>
+ <p>
+ This form can also be used in header files (.hrl) to declare type
+ information for exported functions.
+ Then these header files can be included in files that (implicitly or
+ explicitly) import these functions.
+ </p>
+ <p>
+ For most uses within a given module, the following shorthand suffices:
+ </p>
+ <pre>
-spec Function(ArgType1, ..., ArgTypeN) -> ReturnType.
- </pre>
- <p>
- Also, for documentation purposes, argument names can be given:
- </p>
- <pre>
+ </pre>
+ <p>
+ Also, for documentation purposes, argument names can be given:
+ </p>
+ <pre>
-spec Function(ArgName1 :: Type1, ..., ArgNameN :: TypeN) -> RT.
- </pre>
- <p>
- A function specification can be overloaded.
- That is, it can have several types, separated by a semicolon (<c>;</c>):
- </p>
- <pre>
+ </pre>
+ <p>
+ A function specification can be overloaded.
+ That is, it can have several types, separated by a semicolon (<c>;</c>):
+ </p>
+ <pre>
-spec foo(T1, T2) -> T3
; (T4, T5) -> T6.
- </pre>
- <p>
- A current restriction, which currently results in a warning
- (OBS: not an error) by the compiler, is that the domains of the argument
- types cannot be overlapping.
- For example, the following specification results in a warning:
- </p>
- <pre>
+ </pre>
+ <p>
+ A current restriction, which currently results in a warning
+ (OBS: not an error) by the compiler, is that the domains of
+ the argument types cannot be overlapping.
+ For example, the following specification results in a warning:
+ </p>
+ <pre>
-spec foo(pos_integer()) -> pos_integer()
; (integer()) -> integer().
- </pre>
- <p>
- Type variables can be used in specifications to specify relations for
- the input and output arguments of a function.
- For example, the following specification defines the type of a
- polymorphic identity function:
- </p>
- <pre>
+ </pre>
+ <p>
+ Type variables can be used in specifications to specify relations for
+ the input and output arguments of a function.
+ For example, the following specification defines the type of a
+ polymorphic identity function:
+ </p>
+ <pre>
-spec id(X) -> X.
- </pre>
- <p>
- However, note that the above specification does not restrict the input
- and output type in any way.
- We can constrain these types by guard-like subtype constraints:
- </p>
- <pre>
+ </pre>
+ <p>
+ However, note that the above specification does not restrict the input
+ and output type in any way.
+ We can constrain these types by guard-like subtype constraints:
+ </p>
+ <pre>
-spec id(X) -> X when is_subtype(X, tuple()).
- </pre>
- <p>
- and provide bounded quantification. Currently,
- the <c>is_subtype/2</c> guard is the only guard which can
- be used in a <c>'-spec'</c> attribute.
- </p>
- <p>
- The scope of an <c>is_subtype/2</c> constraint is the
- <c>(...) -> RetType</c>
- specification after which it appears. To avoid confusion,
- we suggest that different variables are used in different constituents of
- an overloaded contract as in the example below:
- </p>
- <pre>
--spec foo({X, integer()}) -> X when is_subtype(X, atom())
- ; ([Y]) -> Y when is_subtype(Y, number()).
- </pre>
- <p>
- Some functions in Erlang are not meant to return;
- either because they define servers or because they are used to
- throw exceptions as the function below:
- </p>
- <pre>
+ </pre>
+ or equivalently by the more succint and more modern form of the above:
+ <pre>
+-spec id(X) -> X when X :: tuple().
+ </pre>
+ <p>
+ and provide bounded quantification. Currently, the <c>::</2> constraint
+ (the <c>is_subtype/2</c> guard) is the only guard constraint which can
+ be used in the <c>'when'</c> part of a <c>'-spec'</c> attribute.
+ </p>
+ <p>
+ The scope of an <c>::</c> constraint is the
+ <c>(...) -> RetType</c>
+ specification after which it appears. To avoid confusion,
+ we suggest that different variables are used in different
+ constituents of an overloaded contract as in the example below:
+ </p>
+ <pre>
+-spec foo({X, integer()}) -> X when X :: atom()
+ ; ([Y]) -> Y when Y :: number().
+ </pre>
+ <p>
+ Some functions in Erlang are not meant to return;
+ either because they define servers or because they are used to
+ throw exceptions as the function below:
+ </p>
+ <pre>
my_error(Err) -> erlang:throw({error, Err}).
- </pre>
- <p>
- For such functions we recommend the use of the special no_return()
- type for their "return", via a contract of the form:
- </p>
- <pre>
+ </pre>
+ <p>
+ For such functions we recommend the use of the special no_return()
+ type for their "return", via a contract of the form:
+ </p>
+ <pre>
-spec my_error(term()) -> no_return().
- </pre>
- </section>
+ </pre>
+ </section>
</chapter>