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Annotation of 42BSD/ucb/lisp/lisplib/manual/ch11.r, revision 1.1

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        !             8:                         CHAPTER  11
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        !            10: 
        !            11:               The Joseph Lister Trace Package
        !            12: 
        !            13: 
        !            14: 
        !            15: 
        !            16:      The Joseph Lister[] Trace package is an important  tool
        !            17: for the interactive debugging of a Lisp program.  It  allows
        !            18: you  to  examine selected  calls to a function or functions,
        !            19: and optionally to stop execution  of  the  Lisp  program  to
        !            20: examine the values of variables.
        !            21: 
        !            22:      The trace package is a set of Lisp programs located  in
        !            23: the    Lisp   program   library   (usually   in   the   file
        !            24: /usr/lib/lisp/trace.l).  Although not normally loaded in the
        !            25: Lisp  system,  the  package will be loaded in when the first
        !            26: call to _t_r_a_c_e is made.
        !            27: 
        !            28: (trace [ls_arg1 ...])
        !            29: 
        !            30:      WHERE:   the form of the ls_arg_i is described below.
        !            31: 
        !            32:      RETURNS: a list of the  function  sucessfully  modified
        !            33:               for  tracing.   If  no  arguments are given to
        !            34:               _t_r_a_c_e, a list of all functions currently being
        !            35:               traced is returned.
        !            36: 
        !            37:      SIDE EFFECT: The function definitions of the  functions
        !            38:                   to trace are modified.
        !            39: 
        !            40: 
        !            41: The ls_arg_i can have one of the following forms:
        !            42: 
        !            43: 
        !            44:   foo - when foo is entered and exited, the  trace  informa-
        !            45:        tion will be printed.
        !            46: 
        !            47: 
        !            48:   (foo break) - when foo is entered  and  exited  the  trace
        !            49:        information  will  be  printed.  Also, just after the
        !            50:        trace information for foo is printed upon entry,  you
        !            51:        will  be put in  a special break loop.  The prompt is
        !            52:        `T>' and you may type any Lisp  expression,  and  see
        !            53:        its  value printed.  The _ith argument to the function
        !            54:        just called can be accessed as (arg _i).  To leave the
        !            55:        trace   loop,  just  type  ^D  or  (tracereturn)  and
        !            56: ____________________
        !            57: 9   []_L_i_s_t_e_r, _J_o_s_e_p_h     1st  Baron  Lister  of  Lyme  Regis,
        !            58: 1827-1912; English surgeon: introduced antiseptic surgery.
        !            59: 
        !            60: 
        !            61: 
        !            62: 9The Joseph Lister Trace Package                         11-1
        !            63: 
        !            64: 
        !            65: 
        !            66: 
        !            67: 
        !            68: 
        !            69: 
        !            70: The Joseph Lister Trace Package                         11-2
        !            71: 
        !            72: 
        !            73:        execution will continue.  Note that ^D will work only
        !            74:        on UNIX systems.
        !            75: 
        !            76: 
        !            77:   (foo if expression) - when foo is entered and the  expres-
        !            78:        sion evaluates to non-nil, then the trace information
        !            79:        will be printed for both exit and entry.  If  expres-
        !            80:        sion evaluates to nil, then no trace information will
        !            81:        be printed.
        !            82: 
        !            83: 
        !            84:   (foo ifnot expression) -  when  foo  is  entered  and  the
        !            85:        expression  evaluates to nil, then the trace informa-
        !            86:        tion will be printed for both  entry  and  exit.   If
        !            87:        both  if and ifnot are specified, then the if expres-
        !            88:        sion must evaluate to non nil AND the  ifnot  expres-
        !            89:        sion  must  evaluate to nil for the trace information
        !            90:        to be printed out.
        !            91: 
        !            92: 
        !            93:   (foo evalin expression) - when foo is  entered  and  after
        !            94:        the  entry  trace  information is printed, expression
        !            95:        will be evaluated. Exit  trace  information  will  be
        !            96:        printed when foo exits.
        !            97: 
        !            98: 
        !            99:   (foo evalout expression) -  when  foo  is  entered,  entry
        !           100:        trace  information  will be printed.  When foo exits,
        !           101:        and before the exit  trace  information  is  printed,
        !           102:        expression will be evaluated.
        !           103: 
        !           104: 
        !           105:   (foo evalinout expression) - this has the same  effect  as
        !           106:        (trace (foo evalin expression evalout expression)).
        !           107: 
        !           108: 
        !           109:   (foo lprint) - this tells _t_r_a_c_e to use the  level  printer
        !           110:        when  printing  the arguments to and the result of  a
        !           111:        call to foo.  The level printer prints only  the  top
        !           112:        levels  of  list structure. Any structure below three
        !           113:        levels is printed as a &.  This allows you  to  trace
        !           114:        functions with massive arguments or results.
        !           115: 
        !           116: 
        !           117: 
        !           118:           The following trace options  permit  one  to  have
        !           119:      greater control over each action which takes place when
        !           120:      a function is traced.  These options are only meant  to
        !           121:      be used by people who need special hooks into the trace
        !           122:      package.  Most people should skip reading this section.
        !           123: 
        !           124: 
        !           125:   (foo traceenter  tefunc)  -  this  tells  _t_r_a_c_e  that  the
        !           126: 
        !           127: 
        !           128:                                       Printed: July 27, 1983
        !           129: 
        !           130: 
        !           131: 
        !           132: 
        !           133: 
        !           134: 
        !           135: 
        !           136: The Joseph Lister Trace Package                         11-3
        !           137: 
        !           138: 
        !           139:        function  to be called when foo is entered is tefunc.
        !           140:        tefunc should be a lambda of two arguments, the first
        !           141:        argument  will  be  bound to the name of the function
        !           142:        being traced, foo in this case.  The second  argument
        !           143:        will  be  bound to the list of arguments to which foo
        !           144:        should be applied.  The function tefunc should  print
        !           145:        some  sort  of "entering foo" message.  It should not
        !           146:        apply foo to the arguments,  however.  That  is  done
        !           147:        later on.
        !           148: 
        !           149: 
        !           150:   (foo traceexit txfunc) - this tells _t_r_a_c_e that  the  func-
        !           151:        tion  to  be  called  when  foo  is exited is txfunc.
        !           152:        txfunc should be a lambda of two arguments, the first
        !           153:        argument  will  be  bound to the name of the function
        !           154:        being traced, foo in this case.  The second  argument
        !           155:        will  be bound to the result of the call to foo.  The
        !           156:        function txfunc should print some  sort  of  "exiting
        !           157:        foo" message.
        !           158: 
        !           159: 
        !           160:   (foo evfcn evfunc) - this tells _t_r_a_c_e that the form evfunc
        !           161:        should  be  evaluated to get the value of foo applied
        !           162:        to its arguments. This option is a bit different from
        !           163:        the  other  special options since evfunc will usually
        !           164:        be an expression, not just the name  of  a  function,
        !           165:        and  that  expression will be specific to the evalua-
        !           166:        tion of  function  foo.   The  argument  list  to  be
        !           167:        applied will be available as T-arglist.
        !           168: 
        !           169: 
        !           170:   (foo printargs prfunc) - this tells _t_r_a_c_e to  used  prfunc
        !           171:        to print the arguments  to be applied to the function
        !           172:        foo.  prfunc should be a lambda of one argument.  You
        !           173:        might  want  to use this option if you wanted a print
        !           174:        function which could  handle  circular  lists.   This
        !           175:        option  will work only if you do not specify your own
        !           176:        traceenter function.  Specifying the option lprint is
        !           177:        just  a simple way of changing the printargs function
        !           178:        to the level printer.
        !           179: 
        !           180: 
        !           181:   (foo printres prfunc) - this tells _t_r_a_c_e to use prfunc  to
        !           182:        print the result of evaluating foo.  prfunc should be
        !           183:        a lambda of one argument.  This option will work only
        !           184:        if  you  do  not specify your own traceexit function.
        !           185:        Specifying the option lprint changes printres to  the
        !           186:        level printer.
        !           187: 
        !           188: 
        !           189: 
        !           190:           You may specify more  than  one  option  for  each
        !           191:      function traced. For example:
        !           192: 
        !           193: 
        !           194:                                       Printed: July 27, 1983
        !           195: 
        !           196: 
        !           197: 
        !           198: 
        !           199: 
        !           200: 
        !           201: 
        !           202: The Joseph Lister Trace Package                         11-4
        !           203: 
        !           204: 
        !           205:      (_t_r_a_c_e (_f_o_o _i_f (_e_q _3 (_a_r_g _1)) _b_r_e_a_k _l_p_r_i_n_t) (_b_a_r _e_v_a_l_i_n
        !           206:      (_p_r_i_n_t _x_y_z_z_y)))
        !           207: 
        !           208:      This tells _t_r_a_c_e to trace two more functions,  foo  and
        !           209:      bar.   Should  foo be called with the first argument _e_q
        !           210:      to 3, then the entering foo  message  will  be  printed
        !           211:      with  the  level  printer.   Next it will enter a trace
        !           212:      break loop, allowing you to evaluate any  lisp  expres-
        !           213:      sions.  When you exit the trace break loop, foo will be
        !           214:      applied to its arguments and the resulting  value  will
        !           215:      be printed, again using the level printer.  Bar is also
        !           216:      traced, and each time bar is entered, an  entering  bar
        !           217:      message  will  be  printed  and then the value of xyzzy
        !           218:      will be printed.  Next bar will be applied to its argu-
        !           219:      ments  and  the  result  will  be printed.  If you tell
        !           220:      _t_r_a_c_e to trace a function which is already  traced,  it
        !           221:      will  first  _u_n_t_r_a_c_e  it.   Thus if you want to specify
        !           222:      more than one trace option for a function, you must  do
        !           223:      it all at once.  The following is _n_o_t equivalent to the
        !           224:      preceding call to _t_r_a_c_e for foo:
        !           225: 
        !           226:      (_t_r_a_c_e (_f_o_o  _i_f  (_e_q  _3  (_a_r_g  _1)))  (_f_o_o  _b_r_e_a_k)  (_f_o_o
        !           227:      _l_p_r_i_n_t))
        !           228: 
        !           229:      In this example, only the last option, lprint, will  be
        !           230:      in effect.
        !           231: 
        !           232:           If the symbol $tracemute is given a non nil value,
        !           233:      printing  of  the  function name and arguments on entry
        !           234:      and exit will be surpressed.  This is particularly use-
        !           235:      ful  if  the  function you are tracing fails after many
        !           236:      calls to it.  In this case  you  would  tell  _t_r_a_c_e  to
        !           237:      trace  the function, set $tracemute to t, and begin the
        !           238:      computation.  When an error occurs  you  can  use  _t_r_a_-
        !           239:      _c_e_d_u_m_p to print out the current trace frames.
        !           240: 
        !           241:           Generally the trace package has its  own  internal
        !           242:      names  for  the the lisp functions it uses, so that you
        !           243:      can feel free to trace system functions like  _c_o_n_d  and
        !           244:      not worry about adverse interaction with the actions of
        !           245:      the trace package.  You can trace any type of function:
        !           246:      lambda,  nlambda,  lexpr  or  macro whether compiled or
        !           247:      interpreted and you can  even  trace  array  references
        !           248:      (however  you  should  not attempt to store in an array
        !           249:      which has been traced).
        !           250: 
        !           251:           When tracing compiled code keep in mind that  many
        !           252:      function  calls  are  translated  directly  to  machine
        !           253:      language  or other equivalent  function calls.  A  full
        !           254:      list of open coded functions is listed at the beginning
        !           255:      of  the  liszt  compiler  source.   _T_r_a_c_e  will  do   a
        !           256:      (_s_s_t_a_t_u_s _t_r_a_n_s_l_i_n_k _n_i_l)  to  insure that the new traced
        !           257:      definitions it defines are called instead  of  the  old
        !           258: 
        !           259: 
        !           260:                                       Printed: July 27, 1983
        !           261: 
        !           262: 
        !           263: 
        !           264: 
        !           265: 
        !           266: 
        !           267: 
        !           268: The Joseph Lister Trace Package                         11-5
        !           269: 
        !           270: 
        !           271:      untraced  ones.  You may notice that compiled code will
        !           272:      run slower after this is done.
        !           273: 
        !           274: (traceargs s_func [x_level])
        !           275: 
        !           276:      WHERE:   if x_level is missing it is assumed to be 1.
        !           277: 
        !           278:      RETURNS: the arguments to the x_level_t_h call to  traced
        !           279:               function s_func are returned.
        !           280: 
        !           281: (tracedump)
        !           282: 
        !           283:      SIDE EFFECT: the  currently  active  trace  frames  are
        !           284:                   printed  on  the terminal.  returns a list
        !           285:                   of functions untraced.
        !           286: 
        !           287: (untrace [s_arg1 ...])
        !           288: 
        !           289:      RETURNS: a list of the functions which were untraced.
        !           290: 
        !           291:      NOTE: if no arguments  are  given,  all  functions  are
        !           292:            untraced.
        !           293: 
        !           294:      SIDE EFFECT: the old function definitions of all traced
        !           295:                   functions  are restored except in the case
        !           296:                   where it appears that the current  defini-
        !           297:                   tion  of  a  function  was  not created by
        !           298:                   trace.
        !           299: 
        !           300: 
        !           301: 
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        !           307: 
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        !           320: 
        !           321: 
        !           322: 
        !           323: 9
        !           324: 
        !           325: 9                                      Printed: July 27, 1983
        !           326: 
        !           327: 
        !           328: 

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