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Annotation of 42BSD/ucb/lisp/lisplib/manual/chb.r, revision 1.1

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        !             8:                         APPENDIX  B
        !             9: 
        !            10: 
        !            11:                       Special Symbols
        !            12: 
        !            13: 
        !            14: 
        !            15: 
        !            16:      The values of these symbols  have a predefined meaning.
        !            17: Some values are counters while others are simply flags whose
        !            18: value the user can change to affect the  operation  of  lisp
        !            19: system.   In all cases, only the value cell of the symbol is
        !            20: important, the function cell is not.  The value of  some  of
        !            21: the  symbols  (like ER%misc) are functions - what this means
        !            22: is that the value cell of those symbols  either  contains  a
        !            23: lambda  expression,  a binary object, or symbol with a func-
        !            24: tion binding.
        !            25: 
        !            26:      The values of the special symbols are:
        !            27: 
        !            28: $gccount$ - The number of  garbage  collections  which  have
        !            29:      occurred.
        !            30: 
        !            31: $gcprint - If bound to  a non nil  value,  then  after  each
        !            32:      garbage  collection and subsequent storage allocation a
        !            33:      summary of storage allocation will be printed.
        !            34: 
        !            35: $ldprint - If bound to a non nil  value,  then  during  each
        !            36:      _f_a_s_l or _c_f_a_s_l a diagnostic message will be printed.
        !            37: 
        !            38: ER%all - The function which is the  error  handler  for  all
        !            39:      errors (see 10)
        !            40: 
        !            41: ER%brk - The function which is the  handler  for  the  error
        !            42:      signal  generated  by the evaluation of the _b_r_e_a_k func-
        !            43:      tion (see 10).
        !            44: 
        !            45: ER%err - The function which is the  handler  for  the  error
        !            46:      signal  generated by the evaluation of the _e_r_r function
        !            47:      (see 10).
        !            48: 
        !            49: ER%misc - The function which is the  handler  of  the  error
        !            50:      signal generated by one of the unclassified errors (see
        !            51:      10).  Most errors are unclassified at this point.
        !            52: 
        !            53: ER%tpl - The function which is the handler to be called when
        !            54:      an  error  has occurred which has not been handled (see
        !            55:      10).
        !            56: 
        !            57: ER%undef - The function which is the handler for  the  error
        !            58:      signal  generated  when a call to an undefined function
        !            59:      is made.
        !            60: 9
        !            61: 
        !            62: 9                                                         B-1
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        !            70:                                                          B-2
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        !            72: 
        !            73: ^w - When bound to a non nil value this will prevent  output
        !            74:      to  the standard output port (poport) from reaching the
        !            75:      standard output (usually a terminal).  Note that ^w  is
        !            76:      a  two character symbol and should not be confused with
        !            77:      ^W which is how we would denote control-w.   The  value
        !            78:      of  ^w  is  checked  when the standard output buffer is
        !            79:      flushed which occurs after a _t_e_r_p_r, _d_r_a_i_n or  when  the
        !            80:      buffer  overflows.   This is most useful in conjunction
        !            81:      with ptport described  below.   System  error  handlers
        !            82:      rebind  ^w  to nil when they are invoked to assure that
        !            83:      error messages are not lost.  (This was introduced  for
        !            84:      Maclisp compatibility).
        !            85: 
        !            86: defmacro-for-compiling - The has an effect  during  compila-
        !            87:      tion.  If  non-nil it causes macros defined by defmacro
        !            88:      to be compiled and included in the object file.
        !            89: 
        !            90: environment - The UNIX environment in assoc list form.
        !            91: 
        !            92: errlist - When a _r_e_s_e_t is done,  the  value  of  errlist  is
        !            93:      saved  away  and  control  is  thrown to the top level.
        !            94:      _E_v_a_l is then mapped over the saved away value  of  this
        !            95:      list.
        !            96: 
        !            97: errport - This port is initially bound to the standard error
        !            98:      file.
        !            99: 
        !           100: evalhook - The value of this symbol, if bound, is  the  name
        !           101:      of a function to handle evalhook traps (see 14.4)
        !           102: 
        !           103: float-format - The value of this symbol is a string which is
        !           104:      the  format  to be used by print to print flonums.  See
        !           105:      the documentation on the UNIX  function  printf  for  a
        !           106:      list of allowable formats.
        !           107: 
        !           108: funcallhook - The value of this symbol,  if  bound,  is  the
        !           109:      name  of  a  function  to handle funcallhook traps (see
        !           110:      14.4).
        !           111: 
        !           112: gcdisable - If non nil, then garbage collections will not be
        !           113:      done  automatically  when  a collectable data type runs
        !           114:      out.
        !           115: 
        !           116: ibase - This is the input radix used by the lisp reader.  It
        !           117:      may  be  either  eight  or  ten.  Numbers followed by a
        !           118:      decimal point are assumed to be decimal  regardless  of
        !           119:      what ibase is.
        !           120: 
        !           121: linel - The line length used  by  the  pretty  printer,  pp.
        !           122:      This  should  be  used  by  _p_r_i_n_t but it is not at this
        !           123:      time.
        !           124: 
        !           125: nil - This symbol represents the null list and thus  can  be
        !           126: 
        !           127: 
        !           128:                                       Printed: July 21, 1983
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        !           136:                                                          B-3
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        !           138: 
        !           139:      written  ().   Its value is always nil.  Any attempt to
        !           140:      change the value will result in an error.
        !           141: 
        !           142: piport - Initially bound to the standard input (usually  the
        !           143:      keyboard).  A read with no arguments reads from piport.
        !           144: 
        !           145: poport - Initially bound to the standard output (usually the
        !           146:      terminal  console).   A  print  with no second argument
        !           147:      writes to poport.  See also: ^w and ptport.
        !           148: 
        !           149: prinlength - If this is a positive fixnum,  then  the  _p_r_i_n_t
        !           150:      function will print no more than prinlength elements of
        !           151:      a list or hunk  and  further  elements  abbreviated  as
        !           152:      `...'.  The initial value of prinlength is nil.
        !           153: 
        !           154: prinlevel - If this is a positive  fixnum,  then  the  _p_r_i_n_t
        !           155:      function  will  print  only  prinlevel levels of nested
        !           156:      lists or hunks.  Lists below this level will be  abbre-
        !           157:      viated by `&' and hunks below this level will be abbre-
        !           158:      viated by a `%'.  The initial  value  of  prinlevel  is
        !           159:      nil.
        !           160: 
        !           161: ptport - Initially bound to nil.  If bound to a  port,  then
        !           162:      all  output  sent  to  the standard output will also be
        !           163:      sent to this port as long as this port is not also  the
        !           164:      standard  output  (as  this  would cause a loop).  Note
        !           165:      that ptport will not get a copy of whatever is sent  to
        !           166:      poport if poport is not bound to the standard output.
        !           167: 
        !           168: readtable - The value of this is the current readtable.   It
        !           169:      is  an array but you should NOT try to change the value
        !           170:      of the elements of the array using the array functions.
        !           171:      This  is because the readtable is an array of bytes and
        !           172:      the smallest unit the array functions work  with  is  a
        !           173:      full  word  (4 bytes).  You can use _s_e_t_s_y_n_t_a_x to change
        !           174:      the values and (_s_t_a_t_u_s _s_y_n_t_a_x ...) to read the values.
        !           175: 
        !           176: t - This symbol always has the value t.  It is  possible  to
        !           177:      change  the  value  of this symbol for short periods of
        !           178:      time but you are strongly advised against it.
        !           179: 
        !           180: top-level - In       a       lisp       system       without
        !           181:      /usr/lib/lisp/toplevel.l loaded, after a _r_e_s_e_t is done,
        !           182:      the lisp system will _f_u_n_c_a_l_l the value of top-level  if
        !           183:      it  is  non  nil.   This provides a way for the user to
        !           184:      introduce  his  own  top   level   interpreter.    When
        !           185:      /usr/lib/lisp/toplevel.l  is  loaded, it sets top-level
        !           186:      to franz-top-level and changes the  _r_e_s_e_t  function  so
        !           187:      that once franz-top-level starts, it cannot be replaced
        !           188:      by changing top-level.  Franz-top-level  does provide a
        !           189:      way  of  changing  the  top  level however, and that is
        !           190:      through user-top-level.
        !           191: 9
        !           192: 
        !           193: 9                                      Printed: July 21, 1983
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        !           200: 
        !           201:                                                          B-4
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        !           203: 
        !           204: user-top-level - If this is bound then after  a  _r_e_s_e_t,  the
        !           205:      top  level function will _f_u_n_c_a_l_l the value of this sym-
        !           206:      bol rather than go through a read eval print loop.
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        !           256: 9
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        !           258: 9                                      Printed: July 21, 1983
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