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NAME

       erl_eterm - Functions for Erlang Term Construction

DESCRIPTION

       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.

EXPORTS

       ETERM *erl_cons(head, tail)

              Types:

                 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 *erl_copy_term(term)

              Types:

                 ETERM *term;

              This function creates and returns a copy of the Erlang term term.

       ETERM *erl_element(position, tuple)

              Types:

                 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.

       voiderl_init(NULL, 0)

              Types:

                 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 *erl_hd(list)

              Types:

                 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 *erl_iolist_to_binary(term)

              Types:

                 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
                      ;

       char *erl_iolist_to_string(list)

              Types:

                 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.

       interl_iolist_length(list)

              Types:

                 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.

       interl_length(list)

              Types:

                 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.

       ETERM *erl_mk_atom(string)

              Types:

                 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.

       ETERM *erl_mk_binary(bptr, size)

              Types:

                 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.

       ETERM *erl_mk_empty_list()

              This function creates and returns an empty Erlang list. Note 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;

              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.

       ETERM *erl_mk_float(f)

              Types:

                 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.

       ETERM *erl_mk_int(n)

              Types:

                 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 *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_pid(node, number, serial, creation)

              Types:

                 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.

       ETERM *erl_mk_port(node, number, creation)

              Types:

                 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.

       ETERM *erl_mk_ref(node, number, creation)

              Types:

                 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.

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

              Types:

                 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.

       ETERM *erl_mk_string(string)

              Types:

                 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 *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 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.

       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.

              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.

       ETERM *erl_mk_var(name)

              Types:

                 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.

       interl_print_term(stream, term)

              Types:

                 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.

       voiderl_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 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.

       interl_size(term)

              Types:

                 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 *erl_tl(list)

              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 *erl_var_content(term, name)

              Types:

                 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.