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NAME

       erl_eterm - Functions for Erlang term construction.

DESCRIPTION

   Note:
       The support for VxWorks is deprecated as of OTP 22, and will be removed in OTP 23.

   Note:
       The  old legacy erl_interface library (functions with prefix erl_) is deprecated as of OTP
       22, and will be removed in OTP 23. This does not apply to the ei library.  Reasonably  new
       gcc  compilers will issue deprecation warnings. In order to disable these warnings, define
       the macro EI_NO_DEPR_WARN.

       This module provides 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, 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.

         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() likely results in garbage.

         char *ERL_ATOM_PTR(t):

         char *ERL_ATOM_PTR_UTF8(t):
           A string representing atom t.

         int ERL_ATOM_SIZE(t):

         int ERL_ATOM_SIZE_UTF8(t):
           The length (in bytes) 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):

         ETERM *ERL_PID_NODE_UTF8(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):

         ETERM *ERL_PORT_NODE_UTF8(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.

EXPORTS

       ETERM *erl_cons(head, tail)

              Types:

                 ETERM *head;
                 ETERM *tail;

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

                * head is the new term to be added.

                * tail is the existing list to which head is 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) do the same thing, but
              check that the argument really is a list.

              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 *erl_copy_term(term)

              Types:

                 ETERM *term;

              Creates and returns a copy of the Erlang term term.

       ETERM *erl_element(position, tuple)

              Types:

                 int position;
                 ETERM *tuple;

              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.

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

       ETERM *erl_hd(list)

              Types:

                 ETERM *list;

              Extracts the first element from a list.

              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 list was not a list.

       void erl_init(NULL, 0)

              Types:

                 void *NULL;
                 int 0;

              This  function must be called before any of the others in the Erl_Interface library
              to  initialize  the  library  functions.  The  arguments  must  be   specified   as
              erl_init(NULL,0).

       int erl_iolist_length(list)

              Types:

                 ETERM *list;

              Returns the length of an I/O list.

              list is an Erlang term containing an I/O list.

              Returns the length of list, or -1 if list 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)

              Types:

                 ETERM *list;

              Converts an I/O list to a binary term.

              list is an Erlang term containing a list.

              Returns an Erlang binary term, or NULL if list 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:

              iolist ::= []
                      |   Binary
                      |   [iohead | iolist]
                      ;
              iohead ::= Binary
                      |   Byte (integer in the range [0..255])
                      |   iolist
                      ;

       char *erl_iolist_to_string(list)

              Types:

                 ETERM *list;

              Converts an I/O list to a NULL-terminated C string.

              list 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 list is
              not an I/O list, or if list contains the integer 0, NULL is  returned.  It  is  the
              caller's responsibility to free the allocated buffer with erl_free().

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

       int erl_length(list)

              Types:

                 ETERM *list;

              Determines the length of a proper list.

              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 list is not a proper list.

       ETERM *erl_mk_atom(string)

              Types:

                 const 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.  Notice  that  it  is  the  caller's
              responsibility to ensure that string contains a valid name for an atom.

              ERL_ATOM_PTR(atom)  and  ERL_ATOM_PTR_UTF8(atom)  can  be used to retrieve the atom
              name     (as     a     NULL-terminated     string).     ERL_ATOM_SIZE(atom)     and
              ERL_ATOM_SIZE_UTF8(atom) return the length of the atom name.

          Note:
              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)

              Types:

                 char *bptr;
                 int size;

              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.

              Returns an Erlang binary object.

              ERL_BIN_PTR(bin)  retrieves  a  pointer  to  the  binary  data.   ERL_BIN_SIZE(bin)
              retrieves the size.

       ETERM *erl_mk_empty_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)

              Types:

                 char *string;
                 int len;

              Creates a list from a sequence of bytes.

                * string is a buffer containing a sequence of bytes. The buffer does not need  to
                  be NULL-terminated.

                * len is the length of string.

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

       ETERM *erl_mk_float(f)

              Types:

                 double f;

              Creates an Erlang float.

              f is a value to be converted to an Erlang float.

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

              ERL_FLOAT_VALUE(t) can be used to retrieve the value from an Erlang float.

       ETERM *erl_mk_int(n)

              Types:

                 int n;

              Creates an Erlang integer.

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

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

              ERL_INT_VALUE(t) can be used to retrieve the value from an Erlang integer.

       ETERM *erl_mk_list(array, arrsize)

              Types:

                 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.

       ETERM *erl_mk_long_ref(node, n1, n2, n3, creation)

              Types:

                 const char *node;
                 unsigned int n1, n2, n3;
                 unsigned int creation;

              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 is to be
                  chosen uniquely for each reference created for a given C-node.

                * creation is an arbitrary number.

              Notice that n3 and creation are limited in precision, so only the low 18 and 2 bits
              of these numbers are used.

              Returns an Erlang reference object.

              ERL_REF_NODE(ref),        ERL_REF_NUMBERS(ref),        ERL_REF_LEN(ref),        and
              ERL_REF_CREATION(ref)  can  be  used  to  retrieve  the  values  used to create the
              reference.

       ETERM *erl_mk_pid(node, number, serial, creation)

              Types:

                 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.

                * node is the name of the C-node.

                * number,  serial,  and  creation  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.

              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.

       ETERM *erl_mk_port(node, number, creation)

              Types:

                 const char *node;
                 unsigned int number;
                 unsigned int creation;

              Creates an Erlang port identifier.

                * node is the name of the C-node.

                * number  and  creation  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.

              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.

       ETERM *erl_mk_ref(node, number, creation)

              Types:

                 const char *node;
                 unsigned int number;
                 unsigned int creation;

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

                * node is the name of the C-node.

                * number is to be chosen uniquely for each reference created for a given C-node.

                * creation is an arbitrary number.

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

              Returns an Erlang reference object.

              ERL_REF_NODE(ref), ERL_REF_NUMBER(ref), and ERL_REF_CREATION(ref) can  be  used  to
              retrieve the three values used to create the reference.

       ETERM *erl_mk_string(string)

              Types:

                 char *string;

              Creates a list from a NULL-terminated string.

              string is a NULL-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)

              Types:

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

       ETERM *erl_mk_uint(n)

              Types:

                 unsigned int n;

              Creates an Erlang unsigned integer.

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

              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.

       ETERM *erl_mk_var(name)

              Types:

                 char *name;

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

              name specifies a name for the variable.

              Returns an Erlang variable object with the name name.

       int erl_print_term(stream, term)

              Types:

                 FILE *stream;
                 ETERM *term;

              Prints the specified Erlang term to the specified output stream.

                * stream indicates where the function is to send its output.

                * term is the Erlang term to print.

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

       void erl_set_compat_rel(release_number)

              Types:

                 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 Erlang/OTP R10 is not compatible with an
              Erlang emulator from Erlang/OTP R9 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
              function erl_init().

          Warning:
              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.

       int erl_size(term)

              Types:

                 ETERM *term;

              Returns  either  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.

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

       ETERM *erl_tl(list)

              Types:

                 ETERM *list;

              Extracts the tail from a list.

              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 list was not a list.

       ETERM *erl_var_content(term, name)

              Types:

                 ETERM *term;
                 char *name;

              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 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.

                * 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 is found in term, or if term  is  not  a  valid  Erlang
              term, NULL is returned.