erl_eterm
This module contains functions for creating and manipulating Erlang terms.
An Erlang term is represented by a C structure of type
ETERM
. Applications should not reference any fields in this
structure directly, because it may be changed in future releases
to provide faster and more compact term storage. Instead,
applications should us the macros and functions provided.
The following macros each take a single ETERM pointer as an argument. They return a non-zero value if the test is true, and 0 otherwise:
ERL_IS_INTEGER(t)
- True if
t
is an integer. ERL_IS_UNSIGNED_INTEGER(t)
- True if
t
is an integer. ERL_IS_FLOAT(t)
- True if
t
is a floating point number. ERL_IS_ATOM(t)
- True if
t
is an atom. ERL_IS_PID(t)
- True if
t
is a Pid (process identifier). ERL_IS_PORT(t)
- True if
t
is a port. ERL_IS_REF(t)
- True if
t
is a reference. ERL_IS_TUPLE(t)
- True if
t
is a tuple. ERL_IS_BINARY(t)
- True if
t
is a binary. ERL_IS_LIST(t)
- True if
t
is a list with zero or more elements. ERL_IS_EMPTY_LIST(t)
- True if
t
is an empty list. ERL_IS_CONS(t)
- True if
t
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() will likely result in garbage.
char *ERL_ATOM_PTR(t)
- A string representing atom
t
. int ERL_ATOM_SIZE(t)
- The length (in characters) of atom t.
void *ERL_BIN_PTR(t)
- A pointer to the contents of
t
int ERL_BIN_SIZE(t)
- The length (in bytes) of binary object
t
. int ERL_INT_VALUE(t)
- The integer of
t
. unsigned int ERL_INT_UVALUE(t)
- The unsigned integer value of
t
. double ERL_FLOAT_VALUE(t)
- The floating point value of
t
. ETERM *ERL_PID_NODE(t)
- The Node in pid
t
. int ERL_PID_NUMBER(t)
- The sequence number in pid
t
. int ERL_PID_SERIAL(t)
- The serial number in pid
t
. int ERL_PID_CREATION(t)
- The creation number in pid
t
. int ERL_PORT_NUMBER(t)
- The sequence number in port
t
. int ERL_PORT_CREATION(t)
- The creation number in port
t
. ETERM *ERL_PORT_NODE(t)
- The node in port
t
. int ERL_REF_NUMBER(t)
- The first part of the reference number in ref
t
. Use only for compatibility. int ERL_REF_NUMBERS(t)
- Pointer to the array of reference numbers in ref
t
. int ERL_REF_LEN(t)
- The number of used reference numbers in ref
t
. int ERL_REF_CREATION(t)
- The creation number in ref
t
. int ERL_TUPLE_SIZE(t)
- The number of elements in tuple
t
. ETERM *ERL_CONS_HEAD(t)
- The head element of list
t
. ETERM *ERL_CONS_TAIL(t)
- A List representing the tail elements of list
t
.
Functions
ETERM *head;
ETERM *tail;
This function concatenates two Erlang terms, prepending
head
onto tail
and thereby creating a cons
cell.
To make a proper list, tail
should always be a
list or an empty list. Note that NULL is not a valid list.
head
is the new term to be added.
tail
is the existing list to which head
will
be concatenated.
The function returns a new list.
ERL_CONS_HEAD(list)
and ERL_CONS_TAIL(list)
can be used to retrieve the head and tail components
from the list. erl_hd(list)
and erl_tl(list)
will do
the same thing, but check that the argument really is a list.
For example:
ETERM *list,*anAtom,*anInt; anAtom = erl_mk_atom("madonna"); anInt = erl_mk_int(21); list = erl_mk_empty_list(); list = erl_cons(anAtom, list); list = erl_cons(anInt, list); ... /* do some work */ erl_free_compound(list);
ETERM *term;
This function creates and returns a copy of the Erlang term
term
.
int position;
ETERM *tuple;
This function extracts a specified element from an Erlang tuple.
position
specifies which element to retrieve from
tuple
. The elements are numbered starting from 1.
tuple
is an Erlang term containing at least
position
elements.
The function returns a new Erlang term corresponding to the
requested element, or NULL if position
was greater than
the arity of tuple
.
void *NULL;
int 0;
This function must be called before any of the others in
the erl_interface
library in order to initialize the
library functions. The arguments must be specified as
erl_init(NULL,0)
.
ETERM *list;
Extracts the first element from a list.
list
is an Erlang term containing a list.
The function returns an Erlang term corresponding to the
head element in the list, or a NULL pointer if list
was
not a list.
ETERM *list;
This function converts an IO list to a binary term.
list
is an Erlang term containing a list.
This function an Erlang binary term, or NULL if list
was not an IO list.
Informally, an IO list is a deep list of characters and binaries which can be sent to an Erlang port. In BNF, an IO list is formally defined as follows:
iolist ::= [] | Binary | [iohead | iolist] ; iohead ::= Binary | Byte (integer in the range [0..255]) | iolist ;
ETERM *list;
This function converts an IO list to a '\\0' terminated C string.
list
is an Erlang term containing an IO list. The IO
list must not contain the integer 0, since C strings may not
contain this value except as a terminating marker.
This function returns a pointer to a dynamically allocated
buffer containing a string. If list
is not an IO list,
or if list
contains the integer 0, NULL is returned. It
is the caller's responsibility free the allocated buffer
with erl_free()
.
Refer to erl_iolist_to_binary()
for the definition of an
IO list.
ETERM *list;
Returns the length of an IO list.
list
is an Erlang term containing an IO list.
The function returns the length of list
, or -1 if
list
is not an IO list.
Refer to erl_iolist_to_binary()
for the definition of
an IO list.
ETERM *list;
Determines the length of a proper list.
list
is an Erlang term containing 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 list
is not a proper list.
char *string;
Creates an atom.
string
is the sequence of characters that will be
used to create the atom.
Returns an Erlang term containing an atom. Note that it is
the callers responsibility to make sure that string
contains a valid name for an atom.
ERL_ATOM_PTR(atom)
can be used to retrieve the
atom name (as a string). Note that the string is not
0-terminated in the atom. ERL_ATOM_SIZE(atom)
returns
the length of the atom name.
char *bptr;
int size;
This function produces an Erlang binary object from a buffer containing a sequence of bytes.
bptr
is a pointer to a buffer containing data to be converted.
size
indicates the length of bptr
.
The function returns an Erlang binary object.
ERL_BIN_PTR(bin)
retrieves a pointer to
the binary data. ERL_BIN_SIZE(bin)
retrieves the
size.
This function creates and returns an empty Erlang list. Note that NULL is not used to represent an empty list; Use this function instead.
char *string;
int len;
This function creates a list from a sequence of bytes.
string
is a buffer containing a sequence of
bytes. The buffer does not need to be zero-terminated.
len
is the length of string
.
The function returns an Erlang list object corresponding to
the character sequence in string
.
double f;
Creates an Erlang float.
f
is a value to be converted to an Erlang float.
The function returns an Erlang float object with the value
specified in f
.
ERL_FLOAT_VALUE(t)
can be used to retrieve the
value from an Erlang float.
int n;
Creates an Erlang integer.
n
is a value to be converted to an Erlang integer.
The function returns an Erlang integer object with the
value specified in n
.
ERL_INT_VALUE(t)
can be used to retrieve the value
value from an Erlang integer.
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.
array
is an array of Erlang terms.
arrsize
is the number of elements in array
.
The function creates an Erlang list object, whose length
arrsize
and whose elements are taken from the terms in
array
.
const char *node;
unsigned int number;
unsigned int serial;
unsigned int creation;
This function creates an Erlang process identifier. The resulting pid can be used by Erlang processes wishing to communicate with the C node.
node
is the name of the C node.
number
, serial
and creation
are
arbitrary numbers. Note though, that these are limited in
precision, so only the low 15, 3 and 2 bits of these numbers
are actually used.
The function returns an Erlang pid object.
ERL_PID_NODE(pid)
, ERL_PID_NUMBER(pid)
,
ERL_PID_SERIAL(pid)
and ERL_PID_CREATION(pid)
can be used to retrieve the four values used to create the pid.
const char *node;
unsigned int number;
unsigned int creation;
This function creates an Erlang port identifier.
node
is the name of the C node.
number
and creation
are arbitrary numbers.
Note though, that these are limited in
precision, so only the low 18 and 2 bits of these numbers
are actually used.
The function returns an Erlang port object.
ERL_PORT_NODE(port)
, ERL_PORT_NUMBER(port)
and ERL_PORT_CREATION
can be used to retrieve the three
values used to create the port.
const char *node;
unsigned int number;
unsigned int creation;
This function creates an old Erlang reference, with
only 18 bits - use erl_mk_long_ref
instead.
node
is the name of the C node.
number
should be chosen uniquely for each reference
created for a given C node.
creation
is an arbitrary number.
Note that number
and creation
are limited in
precision, so only the low 18 and 2 bits of these numbers
are actually used.
The function returns an Erlang reference object.
ERL_REF_NODE(ref)
, ERL_REF_NUMBER(ref)
, and
ERL_REF_CREATION(ref)
to retrieve the three values used
to create the reference.
const char *node;
unsigned int n1, n2, n3;
unsigned int creation;
This function creates an Erlang reference, with 82 bits.
node
is the name of the C node.
n1
, n2
and n3
can be seen as one big number
n1*2^64+n2*2^32+n3
which should be chosen uniquely for
each reference
created for a given C node.
creation
is an arbitrary number.
Note that n3
and creation
are limited in
precision, so only the low 18 and 2 bits of these numbers
are actually used.
The function returns an Erlang reference object.
ERL_REF_NODE(ref)
, ERL_REF_NUMBERS(ref)
,
ERL_REF_LEN(ref)
and
ERL_REF_CREATION(ref)
to retrieve the values used
to create the reference.
char *string;
This function creates a list from a zero terminated string.
string
is the zero-terminated sequence of characters
(i.e. a C string) from which the list will be created.
The function returns an Erlang list.
ETERM **array;
int arrsize;
Creates an Erlang tuple from an array of Erlang terms.
array
is an array of Erlang terms.
arrsize
is the number of elements in array
.
The function creates an Erlang tuple, whose arity is
size
and whose elements are taken from the terms in
array
.
To retrieve the size of a tuple, either use the
erl_size
function (which checks the type of the checked
term and works for a binary as well as for a tuple), or the
ERL_TUPLE_SIZE(tuple)
returns the arity of a tuple.
erl_size()
will do the same thing, but it checks that
the argument really is a tuple.
erl_element(index,tuple)
returns the element
corresponding to a given position in the tuple.
unsigned int n;
Creates an Erlang unsigned integer.
n
is a value to be converted to an Erlang
unsigned integer.
The function returns an Erlang unsigned integer object with
the value specified in n
.
ERL_INT_UVALUE(t)
can be used to retrieve the
value from an Erlang unsigned integer.
char *name;
This function creates an unbound Erlang variable. The variable can later be bound through pattern matching or assignment.
name
specifies a name for the variable.
The function returns an Erlang variable object with the
name name
.
FILE *stream;
ETERM *term;
This function prints the specified Erlang term to the given output stream.
stream
indicates where the function should send its
output.
term
is the Erlang term to print.
The function returns the number of characters written, or a negative value if there was an error.
unsigned release_number;
By default, the erl_interface
library is only guaranteed
to be compatible with other Erlang/OTP components from the same
release as the erl_interface
library itself. For example,
erl_interface
from the OTP R10 release is not compatible
with an Erlang emulator from the OTP R9 release by default.
A call to erl_set_compat_rel(release_number)
sets the
erl_interface
library in compatibility mode of release
release_number
. Valid range of release_number
is [7, current release]. This makes it possible to
communicate with Erlang/OTP components from earlier releases.
Note!
If this function is called, it may only be called once directly after the call to the erl_init() function.
Warning!
You may run into trouble if this feature is used carelessly. Always make sure 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.
ETERM *term;
Returns the arity of an Erlang tuple, or the number of bytes in an Erlang binary object.
term
is an Erlang tuple or an Erlang binary object.
The function returns the size of term
as described
above, or -1 if term
is not one of the two supported
types.
ETERM *list;
Extracts the tail from a list.
list
is an Erlang term containing a list.
The function returns an Erlang list corresponding to the
original list minus the first element, or NULL pointer if
list
was not a list.
ETERM *term;
char *name;
This function returns the contents of the specified variable in an Erlang term.
term
is an Erlang term. In order for this function
to succeed, term
must 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.
name
is the name of an Erlang variable.
Returns the Erlang object corresponding to the value of
name
in term
. If no variable with the name
name
was found in term
, or if term
is
not a valid Erlang term, NULL is returned.