






                         CHAPTER  7


                      The Lisp Reader






   7.1.  Introduction

           The _r_e_a_d function is responsible for converting a
      stream  of characters into a Lisp expression.  _R_e_a_d is
      table driven and the table it uses is called a  _r_e_a_d_t_-
      _a_b_l_e.  The _p_r_i_n_t function does the inverse of _r_e_a_d; it
      converts a Lisp expression into a  stream  of  charac-
      ters.   Typically the conversion is done in such a way
      that if that stream of characters were read  by  _r_e_a_d,
      the  result  would  be  an expression equal to the one
      _p_r_i_n_t was given.  _P_r_i_n_t must also refer to the  readt-
      able  in  order to determine how to format its output.
      The _e_x_p_l_o_d_e function, which returns a list of  charac-
      ters  rather  than  printing them,  must also refer to
      the readtable.

           A readtable is  created  with  the  _m_a_k_e_r_e_a_d_t_a_b_l_e
      function,  modified  with  the  _s_e_t_s_y_n_t_a_x function and
      interrogated with the _g_e_t_s_y_n_t_a_x function.  The  struc-
      ture  of  a  readtable  is  hidden  from the user  - a
      readtable should only be manipulated  with  the  three
      functions mentioned above.

           There is one distinguished readtable  called  the
      _c_u_r_r_e_n_t  _r_e_a_d_t_a_b_l_e  whose  value determines what _r_e_a_d,
      _p_r_i_n_t and _e_x_p_l_o_d_e do.  The current  readtable  is  the
      value  of  the symbol _r_e_a_d_t_a_b_l_e.  Thus it is  possible
      to rapidly change the current syntax by lambda binding
      a  different  readtable to the symbol _r_e_a_d_t_a_b_l_e.  When
      the binding is undone, the syntax reverts to  its  old
      form.



   7.2.  Syntax Classes

           The readtable describes how each of the 128 ascii
      characters   should  be  treated  by  the  reader  and
      printer.  Each character belongs  to  a  _s_y_n_t_a_x  _c_l_a_s_s
      which has three properties:

      character class -
           Tells what the reader should do when it sees this


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           character.  There are a large number of character
           classes. They are described below.

      separator -
           Most types of tokens the  reader  constructs  are
           one  character  long.   Four  token types have an
           arbitrary length:  number  (1234),  symbol  print
           name   (franz),   escaped   symbol   print   name
           (|franz|), and string ("franz").  The reader  can
           easily  determine  when it has come to the end of
           one of the last two types: it just looks for  the
           matching  delimiter (| or ").  When the reader is
           reading a number or symbol print name,  it  stops
           reading  when  it  comes  to a character with the
           _s_e_p_a_r_a_t_o_r property.  The separator  character  is
           pushed back into the input stream and will be the
           first character read when the  reader  is  called
           again.

      escape -
           Tells the printer when to put  escapes  in  front
           of, or around, a symbol whose print name contains
           this character.  There are  three  possibilities:
           always escape a symbol with this character in it,
           only escape a symbol if this is the only  charac-
           ter  in  the  symbol, and only escape a symbol if
           this  is  the  first  character  in  the  symbol.
           [note:  The  printer  will always escape a symbol
           which, if printed out, would look  like  a  valid
           number.]

           When the Lisp system is built, Lisp code is added
      to  a  C-coded kernel and the result becomes the stan-
      dard lisp system.  The readtable  present  in  the  C-
      coded  kernel,  called the _r_a_w _r_e_a_d_t_a_b_l_e, contains the
      bare necessities for reading in Lisp code.  During the
      construction  of  the  complete Lisp system, a copy is
      made of the raw readtable and then the copy  is  modi-
      fied  by  adding macro characters.  The result is what
      is called the _s_t_a_n_d_a_r_d _r_e_a_d_t_a_b_l_e.  When a  new  readt-
      able  is created with _m_a_k_e_r_e_a_d_t_a_b_l_e, a copy is made of
      either the raw  readtable  or  the  current  readtable
      (which is likely to be the standard readtable).



   7.3.  Reader operations

           The reader has a very simple  algorithm.   It  is
      either  _s_c_a_n_n_i_n_g  for  a token, _c_o_l_l_e_c_t_i_n_g a token, or
      _p_r_o_c_e_s_s_i_n_g a token.  Scanning involves reading charac-
      ters  and throwing away those which don't start tokens
      (such as blanks and tabs).  Collecting means gathering


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      the  characters  which  make up a token into a buffer.
      Processing  may  involve  creating  symbols,  strings,
      lists,  fixnums,  bignums or flonums or calling a user
      written function called a character macro.

           The components of the syntax class determine when
      the  reader  switches between the scanning, collecting
      and processing states.  The reader will continue scan-
      ning  as long as the character class of the characters
      it reads is _c_s_e_p_a_r_a_t_o_r.  When  it  reads  a  character
      whose character class is not _c_s_e_p_a_r_a_t_o_r it stores that
      character in its  buffer  and  begins  the  collecting
      phase.

           If the character class of that first character is
      _c_c_h_a_r_a_c_t_e_r,  _c_n_u_m_b_e_r, _c_p_e_r_i_o_d, or _c_s_i_g_n.  then it will
      continue collecting until it  runs  into  a  character
      whose  syntax class has the _s_e_p_a_r_a_t_o_r property.  (That
      last character will be  pushed  back  into  the  input
      buffer  and  will  be  the  first  character read next
      time.) Now the reader goes into the processing  phase,
      checking  to  see  if the token it read is a number or
      symbol.  It is important to note that  after the first
      character  is  collected  the  component of the syntax
      class which tells the reader to   stop  collecting  is
      the _s_e_p_a_r_a_t_o_r property, not the character class.

           If the character class  of  the  character  which
      stopped  the  scanning  is  not  _c_c_h_a_r_a_c_t_e_r,  _c_n_u_m_b_e_r,
      _c_p_e_r_i_o_d, or _c_s_i_g_n.  then  the  reader  processes  that
      character    immediately.    The   character   classes
      _c_s_i_n_g_l_e-_m_a_c_r_o,  _c_s_i_n_g_l_e-_s_p_l_i_c_i_n_g-_m_a_c_r_o,  and  _c_s_i_n_g_l_e-
      _i_n_f_i_x-_m_a_c_r_o  will act like _c_c_h_a_r_a_c_t_e_r if the following
      token is not a _s_e_p_a_r_a_t_o_r.   The  processing  which  is
      done  for  a  given  character  class  is described in
      detail in the next section.



   7.4.  Character classes


_c_c_h_a_r_a_c_t_e_r    raw readtable:A-Z a-z ^H !#$%&*,/:;<=>?@^_`{}~
            standard readtable:A-Z a-z ^H !$%&*/:;<=>?@^_{}~
      A normal character.


_c_n_u_m_b_e_r                                    raw readtable:0-9
                                      standard readtable:0-9
      This type is a digit. The syntax for an integer  (fix-
      num  or  bignum)  is  a  string  of _c_n_u_m_b_e_r characters
      optionally followed by a _c_p_e_r_i_o_d.  If the  digits  are
      not  followed  by a _c_p_e_r_i_o_d, then they are interpreted


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      in base _i_b_a_s_e which must be eight or ten.  The  syntax
      for  a  floating  point  number is either zero or more
      _c_n_u_m_b_e_r's followed by a _c_p_e_r_i_o_d and then  followed  by
      one  or  more  _c_n_u_m_b_e_r's.  A floating point number may
      also be  an integer or floating point number  followed
      by 'e' or 'd', an optional '+' or '-' and then zero or
      more _c_n_u_m_b_e_r's.


_c_s_i_g_n                                       raw readtable:+-
                                       standard readtable:+-
      A leading sign  for  a  number.  No  other  characters
      should be given this class.


_c_l_e_f_t_-_p_a_r_e_n                                  raw readtable:(
                                        standard readtable:(
      A left parenthesis.  Tells the reader to begin forming
      a list.


_c_r_i_g_h_t_-_p_a_r_e_n                                 raw readtable:)
                                        standard readtable:)
      A right parenthesis.  Tells the  reader  that  it  has
      reached the end of a list.


_c_l_e_f_t_-_b_r_a_c_k_e_t                                raw readtable:[
                                        standard readtable:[
      A left bracket.  Tells the reader that it should begin
      forming a list.  See the description of _c_r_i_g_h_t-_b_r_a_c_k_e_t
      for the difference between  cleft-bracket  and  cleft-
      paren.


_c_r_i_g_h_t_-_b_r_a_c_k_e_t                               raw readtable:]
                                        standard readtable:]
      A right bracket.  A _c_r_i_g_h_t-_b_r_a_c_k_e_t finishes the forma-
      tion of the current list and all enclosing lists until
      it finds one which  begins  with  a  _c_l_e_f_t-_b_r_a_c_k_e_t  or
      until it reaches the top level list.


_c_p_e_r_i_o_d                                      raw readtable:.
                                        standard readtable:.
      The period is used to separate element of a cons  cell
      [e.g.  (a . (b . nil)) is the same as (a b)].  _c_p_e_r_i_o_d
      is also used in numbers as described above.


_c_s_e_p_a_r_a_t_o_r                     raw readtable:^I-^M esc space
                          standard readtable:^I-^M esc space
      Separates tokens.  When the reader is scanning,  these


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      character  are  passed over.  Note: there is a differ-
      ence between the _c_s_e_p_a_r_a_t_o_r character  class  and  the
      _s_e_p_a_r_a_t_o_r property of a syntax class.


_c_s_i_n_g_l_e_-_q_u_o_t_e                                raw readtable:'
                                        standard readtable:'
      This causes _r_e_a_d to be called recursively and the list
      (quote <value read>) to be returned.


_c_s_y_m_b_o_l_-_d_e_l_i_m_i_t_e_r                            raw readtable:|
                                        standard readtable:|
      This causes the reader to begin collecting  characters
      and  to  stop  only  when  another  identical _c_s_y_m_b_o_l-
      _d_e_l_i_m_i_t_e_r is seen. The only way to escape  a  _c_s_y_m_b_o_l-
      _d_e_l_i_m_i_t_e_r within a symbol name is with a _c_e_s_c_a_p_e char-
      acter.  The collected characters are converted into  a
      string which becomes the print name of a symbol.  If a
      symbol with an identical print  name  already  exists,
      then  the  allocation is not done, rather the existing
      symbol is used.


_c_e_s_c_a_p_e                                      raw readtable:\
                                        standard readtable:\
      This causes the  next  character  to  read  in  to  be
      treated  as  a  vcharacter.   A character whose syntax
      class is vcharacter has a character  class  _c_c_h_a_r_a_c_t_e_r
      and  does  not  have the _s_e_p_a_r_a_t_o_r property so it will
      not separate symbols.


_c_s_t_r_i_n_g_-_d_e_l_i_m_i_t_e_r                            raw readtable:"
                                        standard readtable:"
      This is  the  same  as  _c_s_y_m_b_o_l-_d_e_l_i_m_i_t_e_r  except  the
      result is returned as a string instead of a symbol.


_c_s_i_n_g_l_e_-_c_h_a_r_a_c_t_e_r_-_s_y_m_b_o_l                  raw readtable:none
                                     standard readtable:none
      This returns a symbol whose print name is the the sin-
      gle character which has been collected.


_c_m_a_c_r_o                                    raw readtable:none
                                       standard readtable:`,
      The reader calls the macro  function  associated  with
      this  character  and the current readtable, passing it
      no arguments.  The result of the macro is added to the
      structure the reader is building, just as if that form
      were directly read by the  reader.   More  details  on
      macros are provided below.


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_c_s_p_l_i_c_i_n_g_-_m_a_c_r_o                           raw readtable:none
                                       standard readtable:#;
      A _c_s_p_l_i_c_i_n_g-_m_a_c_r_o differs from a _c_m_a_c_r_o in the way the
      result  is incorporated in the structure the reader is
      building.  A _c_s_p_l_i_c_i_n_g-_m_a_c_r_o must  return  a  list  of
      forms (possibly empty).  The reader acts as if it read
      each element of the list itself without the  surround-
      ing parenthesis.


_c_s_i_n_g_l_e_-_m_a_c_r_o                             raw readtable:none
                                     standard readtable:none
      This causes to reader to check the next character.  If
      it is a _c_s_e_p_a_r_a_t_o_r then this acts like a _c_m_a_c_r_o.  Oth-
      erwise, it acts like a _c_c_h_a_r_a_c_t_e_r.


_c_s_i_n_g_l_e_-_s_p_l_i_c_i_n_g_-_m_a_c_r_o                    raw readtable:none
                                     standard readtable:none
      This is triggered like  a  _c_s_i_n_g_l_e-_m_a_c_r_o  however  the
      result is spliced in like a _c_s_p_l_i_c_i_n_g-_m_a_c_r_o.


_c_i_n_f_i_x_-_m_a_c_r_o                              raw readtable:none
                                     standard readtable:none
      This is differs from a _c_m_a_c_r_o in that the macro  func-
      tion is passed a form representing what the reader has
      read so far. The result of the macro replaces what the
      reader had read so far.


_c_s_i_n_g_l_e_-_i_n_f_i_x_-_m_a_c_r_o                       raw readtable:none
                                     standard readtable:none
      This differs from the _c_i_n_f_i_x-_m_a_c_r_o in that  the  macro
      will  only be triggered if the character following the
      _c_s_i_n_g_l_e-_i_n_f_i_x-_m_a_c_r_o character is a _c_s_e_p_a_r_a_t_o_r.


_c_i_l_l_e_g_a_l                 raw readtable:^@-^G^N-^Z^\-^_rubout
                    standard readtable:^@-^G^N-^Z^\-^_rubout
      The characters cause the reader to signal an error  if
      read.



   7.5.  Syntax classes

           The readtable maps each character into  a  syntax
      class.   The  syntax  class  contains  three pieces of
      information: the character class, whether  this  is  a
      separator,  and  the escape properties.  The first two
      properties are used by the reader,  the  last  by  the
      printer  (and  _e_x_p_l_o_d_e).   The initial lisp system has


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      the following syntax classes defined.   The  user  may
      add  syntax  classes  with _a_d_d-_s_y_n_t_a_x-_c_l_a_s_s.  For each
      syntax class, we list the properties of the class  and
      which  characters  have  this syntax class by default.
      More information about each syntax class can be  found
      under  the description of the syntax class's character
      class.

vcharacter    raw readtable:A-Z a-z ^H !#$%&*,/:;<=>?@^_`{}~
_c_c_h_a_r_a_c_t_e_r  standard readtable:A-Z a-z ^H !$%&*/:;<=>?@^_{}~



vnumber                                    raw readtable:0-9
_c_n_u_m_b_e_r                               standard readtable:0-9



vsign                                       raw readtable:+-
_c_s_i_g_n                                  standard readtable:+-



vleft-paren                                  raw readtable:(
_c_l_e_f_t_-_p_a_r_e_n                             standard readtable:(
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r

vright-paren                                 raw readtable:)
_c_r_i_g_h_t_-_p_a_r_e_n                            standard readtable:)
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r

vleft-bracket                                raw readtable:[
_c_l_e_f_t_-_b_r_a_c_k_e_t                           standard readtable:[
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r

vright-bracket                               raw readtable:]
_c_r_i_g_h_t_-_b_r_a_c_k_e_t                          standard readtable:]
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r

vperiod                                      raw readtable:.
_c_p_e_r_i_o_d                                 standard readtable:.
_e_s_c_a_p_e_-_w_h_e_n_-_u_n_i_q_u_e


vseparator                     raw readtable:^I-^M esc space
_c_s_e_p_a_r_a_t_o_r                standard readtable:^I-^M esc space
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r
9

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vsingle-quote                                raw readtable:'
_c_s_i_n_g_l_e_-_q_u_o_t_e                           standard readtable:'
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r

vsymbol-delimiter                            raw readtable:|
_c_s_i_n_g_l_e_-_d_e_l_i_m_i_t_e_r                       standard readtable:|
_e_s_c_a_p_e_-_a_l_w_a_y_s


vescape                                      raw readtable:\
_c_e_s_c_a_p_e                                 standard readtable:\
_e_s_c_a_p_e_-_a_l_w_a_y_s


vstring-delimiter                            raw readtable:"
_c_s_t_r_i_n_g_-_d_e_l_i_m_i_t_e_r                       standard readtable:"
_e_s_c_a_p_e_-_a_l_w_a_y_s


vsingle-character-symbol                  raw readtable:none
_c_s_i_n_g_l_e_-_c_h_a_r_a_c_t_e_r_-_s_y_m_b_o_l             standard readtable:none
_s_e_p_a_r_a_t_o_r


vmacro                                    raw readtable:none
_c_m_a_c_r_o                                 standard readtable:`,
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r

vsplicing-macro                           raw readtable:none
_c_s_p_l_i_c_i_n_g_-_m_a_c_r_o                        standard readtable:#;
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r

vsingle-macro                             raw readtable:none
_c_s_i_n_g_l_e_-_m_a_c_r_o                        standard readtable:none
_e_s_c_a_p_e_-_w_h_e_n_-_u_n_i_q_u_e


vsingle-splicing-macro                    raw readtable:none
_c_s_i_n_g_l_e_-_s_p_l_i_c_i_n_g_-_m_a_c_r_o               standard readtable:none
_e_s_c_a_p_e_-_w_h_e_n_-_u_n_i_q_u_e


vinfix-macro                              raw readtable:none
_c_i_n_f_i_x_-_m_a_c_r_o                         standard readtable:none
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r

vsingle-infix-macro                       raw readtable:none
_c_s_i_n_g_l_e_-_i_n_f_i_x_-_m_a_c_r_o                  standard readtable:none
_e_s_c_a_p_e_-_w_h_e_n_-_u_n_i_q_u_e


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villegal                 raw readtable:^@-^G^N-^Z^\-^_rubout
_c_i_l_l_e_g_a_l            standard readtable:^@-^G^N-^Z^\-^_rubout
_e_s_c_a_p_e_-_a_l_w_a_y_s
_s_e_p_a_r_a_t_o_r



   7.6.  Character Macros

           Character macros are user written functions which
      are  executed  during  the reading process.  The value
      returned by a character macro may or may not  be  used
      by  the reader, depending on the type of macro and the
      value returned.  Character macros are always  attached
      to a single character with the _s_e_t_s_y_n_t_a_x function.



      7.6.1.  Types   There are  three  types  of  character
         macros:  normal,  splicing  and infix.  These types
         differ in the arguments they are given or  in  what
         is done with the result they return.



         7.6.1.1.  Normal

                 A normal macro is passed no arguments.  The
            value  returned by a normal macro is simply used
            by the reader  as  if  it  had  read  the  value
            itself.   Here  is  an  example of a macro which
            returns the abbreviation for a given state.


    ____________________________________________________

    ->(_d_e_f_u_n _s_t_a_t_e_a_b_b_r_e_v _n_i_l
         (_c_d_r (_a_s_s_q (_r_e_a_d) '((_c_a_l_i_f_o_r_n_i_a . _c_a) (_p_e_n_n_s_y_l_v_a_n_i_a . _p_a)))))
    stateabbrev
    -> (_s_e_t_s_y_n_t_a_x '_\! '_v_m_a_c_r_o '_s_t_a_t_e_a_b_b_r_e_v)
    t
    -> '( ! _c_a_l_i_f_o_r_n_i_a ! _w_y_o_m_i_n_g ! _p_e_n_n_s_y_l_v_a_n_i_a)
    (ca nil pa)
    ____________________________________________________



Notice what happened to
 ! _w_y_o_m_i_n_g.  Since it wasn't in the table, the  macro  prob-
ably  didn't  want  to return anything at all, but it had to
return something, and whatever it returned was  put  in  the


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list.   The splicing macro, described next, allows a charac-
ter macro function to return a value that is ignored.



         7.6.1.2.  Splicing

                 The value returned from  a  splicing  macro
            must  be  a  list  or nil.  If the value is nil,
            then the value is ignored, otherwise the  reader
            acts  as  if  it  read  each object in the list.
            Usually the list only contains one  element.  If
            the reader is reading at the top level (i.e. not
            collecting elements of list), then it is illegal
            for  a  splicing  macro  to return more then one
            element in the list.  The major advantage  of  a
            splicing  macro over a normal macro is the abil-
            ity of the splicing macro to return nothing. The
            comment  character  (usually  ;)  is  a splicing
            macro bound to a function which reads to the end
            of the line and always returns nil.  Here is the
            previous example written as a splicing macro


    ____________________________________________________

    -> (_d_e_f_u_n _s_t_a_t_e_a_b_b_r_e_v _n_i_l
          ((_l_a_m_b_d_a (_v_a_l_u_e)
               (_c_o_n_d (_v_a_l_u_e (_l_i_s_t _v_a_l_u_e))
                     (_t _n_i_l)))
           (_c_d_r (_a_s_s_q (_r_e_a_d) '((_c_a_l_i_f_o_r_n_i_a . _c_a) (_p_e_n_n_s_y_l_v_a_n_i_a . _p_a))))))
    -> (_s_e_t_s_y_n_t_a_x '! '_v_s_p_l_i_c_i_n_g-_m_a_c_r_o '_s_t_a_t_e_a_b_b_r_e_v)
    -> '(!_p_e_n_n_s_y_l_v_a_n_i_a ! _f_o_o !_c_a_l_i_f_o_r_n_i_a)
    (pa ca)
    -> '!_f_o_o !_b_a_r !_p_e_n_n_s_y_l_v_a_n_i_a
    pa
    ->
    ____________________________________________________






         7.6.1.3.  Infix

                 Infix macros are passed  a  _c_o_n_c  structure
            representing   what   has   been  read  so  far.
            Briefly, a tconc structure is a single list cell
            whose  car points to a list and whose cdr points
            to  the  last  list  cell  in  that  list.   The
            interpretation   by  the  reader  of  the  value
            returned by  an infix macro depends  on  whether


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The Lisp Reader                                         7-11


            the  macro  is  called  while the reader is con-
            structing a list or whether it is called at  the
            top level of the reader.  If the macro is called
            while a list  is  being  constructed,  then  the
            value  returned  should  be   a tconc structure.
            The car of that structure replaces the  list  of
            elements  that  the  reader has been collecting.
            If the macro is called at  top  level,  then  it
            will  be  passed the value nil, and the value it
            returns should either be nil or a  tconc  struc-
            ture.   If the macro returns nil, then the value
            is ignored and the reader continues to read.  If
            the  macro returns a tconc structure of one ele-
            ment (i.e. whose car is a list of one  element),
            then  that  single  element  is  returned as the
            value of _r_e_a_d.  If the  macro  returns  a  tconc
            structure  of  more  than one element, then that
            list of elements is returned  as  the  value  of
            read.


    ____________________________________________________

    -> (_d_e_f_u_n _p_l_u_s_o_p (_x)
          (_c_o_n_d ((_n_u_l_l _x) (_t_c_o_n_c _n_i_l '_\+))
                (_t (_l_c_o_n_c _n_i_l (_l_i_s_t '_p_l_u_s (_c_a_a_r _x) (_r_e_a_d))))))

    plusop
    -> (_s_e_t_s_y_n_t_a_x '_\+ '_v_i_n_f_i_x-_m_a_c_r_o '_p_l_u_s_o_p)
    t
    -> '(_a + _b)
    (plus a b)
    -> '+
    |+|
    ->
    ____________________________________________________






      7.6.2.  Invocations

              There are  three  different  circumstances  in
         which  you  would like a macro function to be trig-
         gered.

         _A_l_w_a_y_s -
              Whenever the  macro  character  is  seen,  the
              macro should be invoked.  This is accomplished
              by  using  the   character   classes   _c_m_a_c_r_o,
              _c_s_p_l_i_c_i_n_g-_m_a_c_r_o, or _c_i_n_f_i_x-_m_a_c_r_o, and by using


                                      Printed: July 21, 1983







The Lisp Reader                                         7-12


              the _s_e_p_a_r_a_t_o_r property.   The  syntax  classes
              vmacro, vsplicing-macro, and vsingle-macro are
              defined this way.

         _W_h_e_n _f_i_r_s_t -
              The macro should only be  triggered  when  the
              macro  character  is the first character found
              after the scanning process.   A  syntax  class
              for  a _w_h_e_n _f_i_r_s_t macro would be defined using
              _c_m_a_c_r_o, _c_s_p_l_i_c_i_n_g-_m_a_c_r_o, or  _c_i_n_f_i_x-_m_a_c_r_o  and
              not including the _s_e_p_a_r_a_t_o_r property.

         _W_h_e_n _u_n_i_q_u_e -
              The macro should only be  triggered  when  the
              macro  character  is  the  only character col-
              lected in the token collection  phase  of  the
              reader,  i.e  the macro character is preceeded
              by zero or more _c_s_e_p_a_r_a_t_o_rs and followed by  a
              _s_e_p_a_r_a_t_o_r.   A  syntax class for a _w_h_e_n _u_n_i_q_u_e
              macro would be  defined  using  _c_s_i_n_g_l_e-_m_a_c_r_o,
              _c_s_i_n_g_l_e-_s_p_l_i_c_i_n_g-_m_a_c_r_o, or _c_s_i_n_g_l_e-_i_n_f_i_x-_m_a_c_r_o
              and not including the _s_e_p_a_r_a_t_o_r property.  The
              syntax  classes  so defined are vsingle-macro,
              vsingle-splicing-macro,   and   vsingle-infix-
              macro.



   7.7.  Functions

(setsyntax 's_symbol 's_synclass ['ls_func])

     WHERE:   ls_func is the name of a function or a  lambda
              body.

     RETURNS: t

     SIDE EFFECT: S_symbol should be a  symbol  whose  print
                  name  is  only  one character.  The syntax
                  class  for  that  character  is   set   to
                  s_synclass  in  the current readtable.  If
                  s_synclass is  a  class  that  requires  a
                  character macro, then ls_func must be sup-
                  plied.

     NOTE: The symbolic syntax codes are  new  to  Opus  38.
           For  compatibility,  s_synclass can be one of the
           fixnum syntax codes which appeared in older  ver-
           sions of the FRANZ LISP Manual.  This compatibil-
           ity is only temporary: existing code  which  uses
           the fixnum syntax codes should be converted.

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The Lisp Reader                                         7-13


(getsyntax 's_symbol)

     RETURNS: the syntax class of  the  first  character  of
              s_symbol's  print name.  s_symbol's print name
              must be exactly one character long.

     NOTE: This function is new to Opus 38.   It  supercedes
           (_s_t_a_t_u_s _s_y_n_t_a_x) which no longer exists.

(add-syntax-class 's_synclass 'l_properties)

     RETURNS: s_synclass

     SIDE EFFECT: Defines the  syntax  class  s_synclass  to
                  have  properties  l_properties.   The list
                  l_properties should  contain  a  character
                  classes mentioned above.  l_properties may
                  contain  one  of  the  escape  properties:
                  _e_s_c_a_p_e-_a_l_w_a_y_s,    _e_s_c_a_p_e-_w_h_e_n-_u_n_i_q_u_e,   or
                  _e_s_c_a_p_e-_w_h_e_n-_f_i_r_s_t.  l_properties may  con-
                  tain the _s_e_p_a_r_a_t_o_r property.  After a syn-
                  tax  class  has  been  defined  with  _a_d_d-
                  _s_y_n_t_a_x-_c_l_a_s_s,  the  _s_e_t_s_y_n_t_a_x function can
                  be used to  give  characters  that  syntax
                  class.


    ____________________________________________________

    ; Define a non-separating macro character.
    ; This type of macro character is used in UCI-Lisp, and
    ; it corresponds to a  FIRST MACRO in Interlisp
    -> (_a_d_d-_s_y_n_t_a_x-_c_l_a_s_s '_v_u_c_i-_m_a_c_r_o '(_c_m_a_c_r_o _e_s_c_a_p_e-_w_h_e_n-_f_i_r_s_t))
    vuci-macro
    ->
    ____________________________________________________
















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