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Annotation of 43BSDReno/share/doc/ps2/09.lisp/chc.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: .\"    @(#)chc.n       6.1 (Berkeley) 4/29/86
        !             6: .\"
        !             7: ." $Header: /na/franz/doc/RCS/chc.n,v 1.1 83/01/31 07:11:44 jkf Exp $
        !             8: .Ap 3 Short\ Subjects.
        !             9: .sp 2v
        !            10: .tl ''\fB\s+2The Garbage Collector\s0\fP'
        !            11: .pp
        !            12: The garbage collector is invoked automatically whenever a collectable
        !            13: data type runs out.
        !            14: All data types are collectable except strings and atoms are not.
        !            15: After a garbage collection finishes, the collector will call the function 
        !            16: .i gcafter
        !            17: which should be a lambda of one argument.
        !            18: The argument passed to 
        !            19: .i gcafter
        !            20: is the name of the data type which ran out and caused the garbage collection.
        !            21: It is 
        !            22: .i gcafter 's
        !            23: responsibility to 
        !            24: allocate more pages of free space.
        !            25: The default 
        !            26: .i gcafter 
        !            27: makes its decision based on the percentage of space still in 
        !            28: use after the garbage collection.
        !            29: If there is a large percentage of space still in use, 
        !            30: .i gcafter
        !            31: allocates a larger amount of free space than if only a small percentage of
        !            32: space is still in use.
        !            33: The default 
        !            34: .i gcafter
        !            35: will also print a summary of the space in use if the variable 
        !            36: .i $gcprint
        !            37: is non nil.
        !            38: The summary always includes the state of the list and fixnum space and 
        !            39: will include another type if it caused the garbage collection.
        !            40: The type which caused the garbage collection is preceded by an asterisk.
        !            41: .sp 4v
        !            42: .tl ''\s+2\fBDebugging\fP\s0''
        !            43: .pp
        !            44: There are two simple functions to help you debug your programs:
        !            45: .i baktrace 
        !            46: and 
        !            47: .i showstack .
        !            48: When an error occurs (or when you type the interrupt character),
        !            49: you will be left at a break level with the state of the computation
        !            50: frozen in the stack.
        !            51: At this point, calling  the function
        !            52: .i showstack
        !            53: will cause the contents of the lisp evaluation stack to be printed in
        !            54: reverse chronological order (most recent first).
        !            55: When the programs you are running are interpreted or traced, the output
        !            56: of 
        !            57: .i showstack 
        !            58: can be very verbose.
        !            59: The function
        !            60: .i baktrace
        !            61: prints a summary of what 
        !            62: .i showstack 
        !            63: prints.
        !            64: That is, if showstack would print a list, 
        !            65: .i baktrace
        !            66: would only print the first element of the list.
        !            67: If you are running compiled code with the \fI(status\ translink)\fP non
        !            68: nil, then fast links are being made.
        !            69: In this case, 
        !            70: there is not enough information on the stack for 
        !            71: .i showstack
        !            72: and 
        !            73: .i baktrace .
        !            74: Thus, if you are debugging compiled code you should probably do 
        !            75: \fI(sstatus\ translink\ nil)\fP.
        !            76: .pp
        !            77: If the contents of the stack don't tell you enough about your problem, the
        !            78: next thing you may 
        !            79: want to try is to run your program with
        !            80: certain functions traced.
        !            81: You can direct the trace package to stop program execution when it enters
        !            82: a function, allowing you to examine the contents of variables or 
        !            83: call other functions.
        !            84: The trace package is documented in Chapter 11.
        !            85: .pp
        !            86: It is also possible to single step the evaluator and to look at stack
        !            87: frames within lisp.
        !            88: The programs which 
        !            89: perform these actions are described in Chapters 14 and 15.
        !            90: .bp
        !            91: .tl ''\fB\s+2The Interpreter\'s Top Level\s0\fP''
        !            92: .pp
        !            93: The default top level interpreter for Franz, named 
        !            94: .i franz-top-level
        !            95: is defined in /usr/lib/lisp/toplevel.l
        !            96: It is given control when the lisp system starts up because the 
        !            97: variable top-level is bound to the symbol
        !            98: .i franz-top-level .
        !            99: The first action 
        !           100: .i franz-top-level 
        !           101: takes is to print out the name of the current
        !           102: version of the lisp system.
        !           103: Then it loads the file .lisprc from the HOME directory of the person
        !           104: invoking the lisp system if that file exists.
        !           105: The .lisprc file allows you to set up your own defaults, read in files,
        !           106: set up autoloading  or anything else you might want to do to personalize
        !           107: the lisp system.
        !           108: Next, the top level goes into a prompt-read-eval-print loop.
        !           109: Each time around the loop, before printing the prompt it checks 
        !           110: if the variable user-top-level is bound.
        !           111: If so, then the value of user-top-level will be 
        !           112: .i funcall ed.
        !           113: This provides a convenient way for a user to introduce his own top level
        !           114: (Liszt, the lisp compiler, is an example of a program which uses this).
        !           115: If the user types a ^D (which is the end of file character), and  the
        !           116: standard input is not from a keyboard, the lisp system will exit.
        !           117: If the standard input is a keyboard and if the value of 
        !           118: .i "(status\ ignoreeof)"
        !           119: is nil, the lisp system will also exit.
        !           120: Otherwise the end of file will be ignored.
        !           121: When a 
        !           122: .i reset 
        !           123: is done
        !           124: the current value of 
        !           125: .i errlist
        !           126: is saved away and control is thrown back up to the top level where 
        !           127: .i eval
        !           128: is mapped over the saved value of 
        !           129: .i errlist.

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