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Annotation of 43BSDReno/share/doc/ps2/09.lisp/chb.n, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1980 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)chb.n       6.1 (Berkeley) 4/29/86
        !             6: .\"
        !             7: ." $Header: /na/franz/doc/RCS/chb.n,v 1.1 83/01/31 07:11:40 jkf Exp $
        !             8: .Ap 2 Special\ Symbols
        !             9: .pp
        !            10: The values of these symbols  have a predefined meaning.
        !            11: Some values are counters 
        !            12: while others are simply flags whose value the user can change to affect
        !            13: the operation of lisp system.
        !            14: In all cases, only the value cell of the symbol is important, the function
        !            15: cell is not.
        !            16: The value of some of the symbols (like \fBER%misc\fP) 
        !            17: are functions - what this means is that the value cell of those symbols
        !            18: either contains a lambda expression,
        !            19: a binary object,
        !            20: or symbol with a function binding.
        !            21: .pp 
        !            22: The values of the special symbols are:
        !            23: .in .5i
        !            24: .de Sa
        !            25: .sp 1v
        !            26: .ti -.5i
        !            27: \fB\\$1\fP\ \-\ \\
        !            28: ..
        !            29: .Sa $gccount$
        !            30: The number of garbage collections which have occurred.
        !            31: .Sa $gcprint
        !            32: If bound to  a non nil value, then after each garbage collection and 
        !            33: subsequent storage allocation a summary of storage allocation will
        !            34: be printed.
        !            35: .Sa $ldprint
        !            36: If bound to a non nil value, then during each 
        !            37: .i fasl
        !            38: or 
        !            39: .i cfasl
        !            40: a diagnostic message will be printed.
        !            41: .Sa ER%all
        !            42: The function which is the error handler for all errors (see \(sc10)
        !            43: .Sa ER%brk
        !            44: The function which is the handler for the 
        !            45: error signal generated by the evaluation of the 
        !            46: .i break 
        !            47: function (see \(sc10).
        !            48: .Sa ER%err
        !            49: The function which is the handler for the error 
        !            50: signal generated by the evaluation of the
        !            51: .i err
        !            52: function (see \(sc10).
        !            53: .Sa ER%misc
        !            54: The function which is the handler of the error 
        !            55: signal generated by one of the unclassified errors (see \(sc10).
        !            56: Most errors are unclassified at this point.
        !            57: .Sa ER%tpl
        !            58: The function which is the handler to be called
        !            59: when an error has occurred which 
        !            60: has not been handled (see \(sc10). 
        !            61: .Sa ER%undef
        !            62: The function which is the handler for the 
        !            63: error signal generated when a call to an undefined function
        !            64: is made.
        !            65: .Sa ^w
        !            66: When bound to a non nil value this will prevent output to the standard
        !            67: output port (poport) from reaching the standard output (usually a terminal).
        !            68: Note that ^w is a two character symbol and should not be confused
        !            69: with ^W which is how we would denote control-w.
        !            70: The value of ^w is checked when the standard output buffer is flushed
        !            71: which occurs after a 
        !            72: .i terpr , 
        !            73: .i drain 
        !            74: or when the buffer overflows.
        !            75: This is most useful in conjunction with ptport described below.
        !            76: System error handlers rebind ^w to nil when they are invoked to assure
        !            77: that error messages are not lost.
        !            78: (This was introduced for Maclisp compatibility).
        !            79: .Sa defmacro-for-compiling
        !            80: The has an effect during compilation.  
        !            81: If non-nil it causes macros defined by defmacro to be 
        !            82: compiled and included in the
        !            83: object file.
        !            84: .Sa environment
        !            85: The UNIX environment in assoc list form.
        !            86: .Sa errlist
        !            87: When a 
        !            88: .i reset
        !            89: is done, the value of errlist is saved away and control is thrown to
        !            90: the top level.
        !            91: \fIEval\fP
        !            92: is then mapped over the saved away 
        !            93: value of this list.
        !            94: .Sa errport
        !            95: This port is initially bound to the standard error file.
        !            96: .Sa evalhook
        !            97: The value of this symbol, if bound, is the name of a function to handle
        !            98: evalhook traps (see \(sc14.4)
        !            99: .Sa float-format
        !           100: The value of this symbol is a string which is the format to be used
        !           101: by print to print flonums.
        !           102: See the documentation on the UNIX function printf for a list
        !           103: of allowable formats.
        !           104: .Sa funcallhook
        !           105: The value of this symbol, if bound, is the name of a function to handle
        !           106: funcallhook traps (see \(sc14.4).
        !           107: .Sa gcdisable
        !           108: If non nil, then garbage collections will not be done automatically when
        !           109: a collectable data type runs out.
        !           110: .Sa ibase
        !           111: This is the input radix used by the lisp reader.
        !           112: It may be either eight or ten. 
        !           113: Numbers followed by a decimal point are assumed to be decimal regardless
        !           114: of what ibase is.
        !           115: .Sa linel
        !           116: The line length used by the pretty printer, pp.
        !           117: This should be used by 
        !           118: .i print 
        !           119: but it is not at this time.
        !           120: .Sa nil
        !           121: This symbol represents the null list and thus can be written ().
        !           122: Its value is always nil.
        !           123: Any attempt to change the value will result in an error.
        !           124: .Sa piport
        !           125: Initially bound to the standard input (usually the keyboard).
        !           126: A read with no arguments reads from piport.
        !           127: .Sa poport
        !           128: Initially bound to the standard output (usually the terminal console).
        !           129: A print with no second argument writes to poport.
        !           130: See also: ^w and ptport.
        !           131: .Sa prinlength
        !           132: If this is a positive fixnum, then the \fIprint\fP function will print
        !           133: no more than prinlength elements of a list or hunk and further elements
        !           134: abbreviated as `...'.
        !           135: The initial value of prinlength is nil.
        !           136: .Sa prinlevel
        !           137: If this is a positive fixnum, then the \fIprint\fP function will print
        !           138: only prinlevel levels of nested lists or hunks.
        !           139: Lists below this level will be abbreviated by `&' and hunks below this 
        !           140: level will be abbreviated by a `%'.
        !           141: The initial value of prinlevel is nil.
        !           142: .Sa ptport
        !           143: Initially bound to nil.
        !           144: If bound to a port, then all output sent to the standard output will
        !           145: also be sent to this port as long as this port is not also 
        !           146: the standard output (as this would cause a loop).
        !           147: Note that ptport will not get a copy of whatever is sent to poport
        !           148: if poport is not bound to the standard output.
        !           149: .Sa readtable
        !           150: The value of this is the current readtable.
        !           151: It is an array but you should NOT try to change the value of the elements
        !           152: of the array using the array functions.
        !           153: This is because the readtable is an array of bytes and the smallest 
        !           154: unit the array functions work with is a full word (4 bytes).
        !           155: You can use 
        !           156: .i setsyntax 
        !           157: to change the values and
        !           158: .i "(status syntax ...)"
        !           159: to read the values.
        !           160: .Sa t
        !           161: This symbol always has the value t.
        !           162: It is possible to change the value of this symbol for short
        !           163: periods of time but you are strongly advised against it.
        !           164: .Sa top-level
        !           165: In a lisp system without /usr/lib/lisp/toplevel.l loaded, after a 
        !           166: .i reset
        !           167: is done, the lisp system will 
        !           168: .i funcall 
        !           169: the value of top-level if it is
        !           170: non nil.
        !           171: This provides a way for the user to introduce his own top level interpreter.
        !           172: When /usr/lib/lisp/toplevel.l is loaded, it sets top-level to franz-top-level
        !           173: and changes the 
        !           174: .i reset 
        !           175: function so that once franz-top-level starts, it cannot
        !           176: be replaced by changing top-level.
        !           177: Franz-top-level  does provide a way of changing 
        !           178: the top level however, and that is 
        !           179: through user-top-level.
        !           180: .Sa user-top-level
        !           181: If this is bound then after a 
        !           182: .i reset ,
        !           183: the top level function will
        !           184: .i funcall 
        !           185: the value of this symbol rather than go through a read eval print
        !           186: loop.

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