19962016 Ericsson AB. All Rights Reserved. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. erl_eterm Torbjörn Törnkvist Torbjörn Törnkvist Bjarne Däcker Torbjörn Törnkvist 1998-07-03 A erl_eterm.xml
erl_eterm Functions for Erlang term construction.

This module provides functions for creating and manipulating Erlang terms.

An Erlang term is represented by a C structure of type . Applications should not reference any fields in this structure directly, as it can be changed in future releases to provide faster and more compact term storage. Instead, applications should use the macros and functions provided.

Each of the following macros takes a single ETERM pointer as an argument. The macros return a non-zero value if the test is true, otherwise 0.

True if is an integer. True if is an integer. True if is a floating point number. True if is an atom. True if is a pid (process identifier). True if is a port. True if is a reference. True if is a tuple. True if is a binary. True if is a list with zero or more elements. True if is an empty list. True if is a list with at least one element.

The following macros can be used for retrieving parts of Erlang terms. None of these do any type checking. Results are undefined if you pass an ETERM* containing the wrong type. For example, passing a tuple to ERL_ATOM_PTR() likely results in garbage.

A string representing atom . The length (in bytes) of atom . A pointer to the contents of . The length (in bytes) of binary object . The integer of . The unsigned integer value of . The floating point value of . The node in pid . The sequence number in pid . The serial number in pid . The creation number in pid . The sequence number in port . The creation number in port . The node in port . The first part of the reference number in ref . Use only for compatibility. Pointer to the array of reference numbers in ref . The number of used reference numbers in ref . The creation number in ref . The number of elements in tuple . The head element of list . A list representing the tail elements of list . ETERM *erl_cons(head, tail) Prepend a term to the head of a list. ETERM *head; ETERM *tail;

Concatenates two Erlang terms, prepending onto and thereby creating a cell. To make a proper list, is always to be a list or an empty list. Notice that NULL is not a valid list.

is the new term to be added. is the existing list to which is concatenated.

The function returns a new list.

and can be used to retrieve the head and tail components from the list. and do the same thing, but check that the argument really is a list.

Example:

 ETERM *erl_copy_term(term) Create a copy of an Erlang term. ETERM *term;

Creates and returns a copy of the Erlang term .

 ETERM *erl_element(position, tuple) Extract an element from an Erlang tuple. int position; ETERM *tuple;

Extracts a specified element from an Erlang tuple.

specifies which element to retrieve from . The elements are numbered starting from 1. is an Erlang term containing at least elements.

Returns a new Erlang term corresponding to the requested element, or NULL if was greater than the arity of .

 ETERM *erl_hd(list) Extract the first element from a list. ETERM *list;

Extracts the first element from a list.

is an Erlang term containing a list.

Returns an Erlang term corresponding to the head head element in the list, or a NULL pointer if was not a list.

 voiderl_init(NULL, 0) Initialization routine. void *NULL; int 0;

This function must be called before any of the others in the library to initialize the library functions. The arguments must be specified as .

 interl_iolist_length(list) Return the length of an I/O list. ETERM *list;

Returns the length of an I/O list.

is an Erlang term containing an I/O list.

Returns the length of , or -1 if is not an I/O list.

For the definition of an I/O list, see erl_iolist_to_binary.

 ETERM *erl_iolist_to_binary(term) Convert an I/O list to a binary. ETERM *list;

Converts an I/O list to a binary term.

is an Erlang term containing a list.

Returns an Erlang binary term, or NULL if was not an I/O list.

Informally, an I/O list is a deep list of characters and binaries that can be sent to an Erlang port. In BNF, an I/O list is formally defined as follows:

 char *erl_iolist_to_string(list) Convert an I/O list to a zero-terminated string. ETERM *list;

Converts an I/O list to a '\0' terminated C string.

is an Erlang term containing an I/O list. The I/O list must not contain the integer 0, as C strings may not contain this value except as a terminating marker.

Returns a pointer to a dynamically allocated buffer containing a string. If is not an I/O list, or if contains the integer 0, NULL is returned. It is the caller's responsibility to free the allocated buffer with .

For the definition of an I/O list, see erl_iolist_to_binary.

 interl_length(list) Determine the length of a list. ETERM *list;

Determines the length of a proper list.

is an Erlang term containing a proper list. In a proper list, all tails except the last point to another list cell, and the last tail points to an empty list.

Returns -1 if is not a proper list.

 ETERM *erl_mk_atom(string) Create an atom. const char *string;

Creates an atom.

is the sequence of characters that will be used to create the atom.

Returns an Erlang term containing an atom. Notice that it is the caller's responsibility to ensure that contains a valid name for an atom.

and can be used to retrieve the atom name (as a null-terminated string). and return the length of the atom name.

The UTF-8 variants were introduced in Erlang/OTP R16 and the string returned by ERL_ATOM_PTR(atom) was not null-terminated on older releases.

 ETERM *erl_mk_binary(bptr, size) Create a binary object. char *bptr; int size;

Produces an Erlang binary object from a buffer containing a sequence of bytes.

is a pointer to a buffer containing data to be converted. indicates the length of .

Returns an Erlang binary object.

retrieves a pointer to the binary data. retrieves the size.

 ETERM *erl_mk_empty_list() Create an empty Erlang list.

Creates and returns an empty Erlang list. Notice that NULL is not used to represent an empty list; Use this function instead.

 ETERM *erl_mk_estring(string, len) Create an Erlang string. char *string; int len;

Creates a list from a sequence of bytes.

is a buffer containing a sequence of bytes. The buffer does not need to be zero-terminated. is the length of .

Returns an Erlang list object corresponding to the character sequence in .

 ETERM *erl_mk_float(f) Create an Erlang float. double f;

Creates an Erlang float.

is a value to be converted to an Erlang float.

Returns an Erlang float object with the value specified in or if is not finite.

can be used to retrieve the value from an Erlang float.

 ETERM *erl_mk_int(n) Create an Erlang integer. int n;

Creates an Erlang integer.

is a value to be converted to an Erlang integer.

Returns an Erlang integer object with the value specified in .

can be used to retrieve the value from an Erlang integer.

 ETERM *erl_mk_list(array, arrsize) Create a list from an array. ETERM **array; int arrsize;

Creates an Erlang list from an array of Erlang terms, such that each element in the list corresponds to one element in the array.

is an array of Erlang terms. is the number of elements in .

The function creates an Erlang list object, whose length and whose elements are taken from the terms in .

 ETERM *erl_mk_long_ref(node, n1, n2, n3, creation) Create an Erlang reference. const char *node; unsigned int n1, n2, n3; unsigned int creation;

Creates an Erlang reference, with 82 bits.

is the name of the C-node. , , and can be seen as one big number , which is to be chosen uniquely for each reference created for a given C-node. is an arbitrary number.

Notice that and are limited in precision, so only the low 18 and 2 bits of these numbers are used.

Returns an Erlang reference object.

, , , and can be used to retrieve the values used to create the reference.

 ETERM *erl_mk_pid(node, number, serial, creation) Create a process identifier. const char *node; unsigned int number; unsigned int serial; unsigned int creation;

Creates an Erlang process identifier (pid). The resulting pid can be used by Erlang processes wishing to communicate with the C-node.

is the name of the C-node. , , and are arbitrary numbers. Notice that these are limited in precision, so only the low 15, 3, and 2 bits of these numbers are used.

Returns an Erlang pid object.

, , , and can be used to retrieve the four values used to create the pid.

 ETERM *erl_mk_port(node, number, creation) Create a port identifier. const char *node; unsigned int number; unsigned int creation;

Creates an Erlang port identifier.

is the name of the C-node. and are arbitrary numbers. Notice that these are limited in precision, so only the low 18 and 2 bits of these numbers are used.

Returns an Erlang port object.

, , and can be used to retrieve the three values used to create the port.

 ETERM *erl_mk_ref(node, number, creation) Create an old Erlang reference. const char *node; unsigned int number; unsigned int creation;

Creates an old Erlang reference, with only 18 bits - use instead.

is the name of the C-node. is to be chosen uniquely for each reference created for a given C-node. is an arbitrary number.

Notice that and are limited in precision, so only the low 18 and 2 bits of these numbers are used.

Returns an Erlang reference object.

, , and can be used to retrieve the three values used to create the reference.

 ETERM *erl_mk_string(string) Create a string. char *string;

Creates a list from a zero-terminated string.

is the zero-terminated sequence of characters (that is, a C string) from which the list will be created.

Returns an Erlang list.

 ETERM *erl_mk_tuple(array, arrsize) Create an Erlang tuple from an array. ETERM **array; int arrsize;

Creates an Erlang tuple from an array of Erlang terms.

is an array of Erlang terms. is the number of elements in .

The function creates an Erlang tuple, whose arity is and whose elements are taken from the terms in .

To retrieve the size of a tuple, either use function (which checks the type of the checked term and works for a binary as well as for a tuple) or returns the arity of a tuple. does the same thing, but it checks that the argument is a tuple. returns the element corresponding to a given position in the tuple.

 ETERM *erl_mk_uint(n) Create an unsigned integer. unsigned int n;

Creates an Erlang unsigned integer.

is a value to be converted to an Erlang unsigned integer.

Returns an Erlang unsigned integer object with the value specified in .

can be used to retrieve the value from an Erlang unsigned integer.

 ETERM *erl_mk_var(name) Create an Erlang variable. char *name;

Creates an unbound Erlang variable. The variable can later be bound through pattern matching or assignment.

specifies a name for the variable.

Returns an Erlang variable object with the name .

 interl_print_term(stream, term) Print an Erlang term. FILE *stream; ETERM *term;

Prints the specified Erlang term to the specified output stream.

indicates where the function is to send its output. is the Erlang term to print.

Returns the number of characters written on success, otherwise a negative value.

 voiderl_set_compat_rel(release_number) Set the Erl_Interface library in compatibility mode. unsigned release_number;

By default, the library is only guaranteed to be compatible with other Erlang/OTP components from the same release as the library itself. For example, from Erlang/OTP R10 is not compatible with an Erlang emulator from Erlang/OTP R9 by default.

A call to sets the library in compatibility mode of release . Valid range of is [7, current release]. This makes it possible to communicate with Erlang/OTP components from earlier releases.

If this function is called, it may only be called once directly after the call to function erl_init().

You may run into trouble if this feature is used carelessly. Always ensure that all communicating components are either from the same Erlang/OTP release, or from release X and release Y where all components from release Y are in compatibility mode of release X.

 interl_size(term) Return the arity of a tuple or binary. ETERM *term;

Returns either the arity of an Erlang tuple or the number of bytes in an Erlang binary object.

is an Erlang tuple or an Erlang binary object.

Returns the size of as described above, or -1 if is not one of the two supported types.

 ETERM *erl_tl(list) Extract the tail from a list. ETERM *list;

Extracts the tail from a list.

is an Erlang term containing a list.

Returns an Erlang list corresponding to the original list minus the first element, or NULL pointer if was not a list.

 ETERM *erl_var_content(term, name) Extract the content of a variable. ETERM *term; char *name;

Returns the contents of the specified variable in an Erlang term.

is an Erlang term. In order for this function to succeed, must either be an Erlang variable with the specified name, or it must be an Erlang list or tuple containing a variable with the specified name. Other Erlang types cannot contain variables. is the name of an Erlang variable.

Returns the Erlang object corresponding to the value of in . If no variable with the name is found in , or if is not a valid Erlang term, NULL is returned.