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diff --git a/system/doc/reference_manual/typespec.xml b/system/doc/reference_manual/typespec.xml index 52dc0c943e..f08639f9a1 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> @@ -32,29 +32,24 @@ <section> <title>Introduction of Types</title> <p> - Although Erlang is a dynamically typed language this section describes - an extension to the Erlang language for declaring sets of Erlang terms - to form a particular type, effectively forming a specific sub-type of the - set of all Erlang terms. + Erlang is a dynamically typed language. Still, it comes with a + language extension for declaring sets of Erlang terms to form a + particular type, effectively forming a specific sub-type of the set + of all Erlang terms. </p> <p> - Subsequently, these types can be used to specify types of record fields - and the argument and return types of functions. + Subsequently, these types can be used to specify types of record fields + and the argument and return types of functions. </p> <p> - Type information can be used to document function interfaces, - provide more information for bug detection tools such as <c>Dialyzer</c>, - and can be exploited by documentation tools such as <c>Edoc</c> for - generating program documentation of various forms. - It is expected that the type language described in this document will - supersede and replace the purely comment-based <c>@type</c> and + Type information can be used to document function interfaces, + provide more information for bug detection tools such as <c>Dialyzer</c>, + and can be exploited by documentation tools such as <c>Edoc</c> for + generating program documentation of various forms. + It is expected that the type language described in this document will + supersede and replace the purely comment-based <c>@type</c> and <c>@spec</c> declarations used by <c>Edoc</c>. </p> - <warning> - The syntax and semantics described here is still preliminary and might be - slightly changed and extended before it becomes officially supported. - The plan is that this will happen in R14B. - </warning> </section> <section> <marker id="syntax"></marker> @@ -139,326 +134,334 @@ 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>boolean()</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> +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> 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> +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> Record :: #Erlang_Atom{} - | #Erlang_Atom{Fields} - </pre> + | #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> - 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> --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> --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> --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> --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> + 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> + 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> + <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 not accessible by other modules anyway - 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> +-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> +-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> -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> -#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> -#rec{some_field :: Type} - </pre> - <p> - Any unspecified fields are assumed to have the type in the original - record declaration. - </p> - </section> + 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> +#rec{some_field :: Type}</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> --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> --spec Function(ArgType1, ..., ArgTypeN) -> ReturnType. - </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> + <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 suffices: + </p> + <pre> +-spec Function(ArgType1, ..., ArgTypeN) -> ReturnType.</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> -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> + ; (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> -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> --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> --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> -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> --spec my_error(term()) -> no_return(). - </pre> - </section> + ; (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> +-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> +-spec id(X) -> X when is_subtype(X, tuple()).</pre> + <p> + or equivalently by the more succinct and more modern form of the above: + </p> + <pre> +-spec id(X) -> X when X :: tuple().</pre> + <p> + and provide bounded quantification. Currently, the <c>::</c> 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> +-spec my_error(term()) -> no_return().</pre> + </section> </chapter> |