perm filename LEAP.WRU[NEW,AIL] blob sn#408201 filedate 1979-01-08 generic text, type T, neo UTF8

				by K. Pingle

	Modified FALL 1972 to reflect changes by Jim Low

WARNING:  This document is rated X and is only for the use of adults
	with very strong stomachs.  It is provided for people who
	have to debug leap programs so they have some idea of what
	is being done to them and the data structures they might
	want to look at.  The facts provided here are NOT sufficient
	to allow hackers to modify things from their programs.  The
	information provided may change, or become incorrect, at
	any time.


	When initialized,   SAIL creates  a user  table in your  core
image with  information for the runtime routines.   This table, whose
address is contained in the cell named GOGTAB, is normally  placed in
an AC('15) when leap is called  and indexed into.  The global model's
table  is always in a  fixed location starting at  GLUSER. If you are
inside LEAP, or have just left it, a pointer to the  user table is in
AC '15.   If it is,  or  was,  a global model  operation (see bits in
section 2), a pointer to GLUSER is in  AC 7.  Below is a list of  the
more interesting entries in the user table.  Be warned that the index
may  change at any time.  SAIL programs refering  to these quantities
should use the USERCON pseudo function instead of fixed octal indices
Those entries with  *** following the index also have  meaning in the
global user table

****		*****	********************************************

0		UUO1	This is the return address for the last call
			of LEAP, which was cleverly removed from the
			stack so you couldn't find it.

303		PDL	IOWD SIZE,BASE  -  the initial system pdl

304		SPDL	IOWD SIZE,BASE  -  the intial string pdl

306 ***		MAXITM	The current top item number (low number for
			global items)

307 ***		OLDITM	A linked list of deleted items of the form
			XWD item #,pointer to next word of list

310 ***		INFOTAB Points to a table with information on each item.
			A more complete description will be given later.
311 ***		DATAB	Points to a table with the datums of each item,
			indexed by item number. The entry for an item
			contains a numerical value, array descriptor,
			a pointer to a set, or zero if there is no datum.
			A pointer to the table can also be found in cell
			DATM in your core image.  GDATM contains the
			pointer for global datums.

312 ***		HASTAB	Pointer to a 512 word long (default length) long
			hash table for associations.  More will be said
			about it later.

313 ***		FP1	One word free list  with right half  of each
			cell pointing at the next one.  FP1 is of the
			form XWD end of list,start of list. Used for
			sets and various other one word free cells.

314 ***		FP2	Pointer to two word free list for associations.
			The right half of the first word of each pair
			points to the first word of the next pair.

316		HASHP	XWD list of free string descriptors,,pointer to
			printname hash table. More about this later.

317		MKBP	Address of make - breakpoint procedure or 0
			if none.

320		ERBP    Address of ERASE - breakpoint procedure or 0 if none

324		LEABOT	A 86 word long array search control block, or
			SCB, used for retrieving associations by the
			derived set,  association existance  test,
			bracketed triple item retrieval,  and erase
			operations.  The SCB will be described later.

325		FRLOC	Points to the current SCB (for the FOREACH
                        statement we are currently executing) or zero
			if we are not in a FOREACH. The left half
			points to a variable named SCB... of the
			procedure in which the FOREACH resides. SCB...
			is used as a flag to the block exit routine
			(BEXIT) which signals whether a FOREACH wil
			have to be exited before a GO TO out of the
			block is done. FRLOC is only valid if there
			are no processes. If there are processes the
		        information normally in FRLOC is contained 
			in the process variable CURSCB.

326		SCBCHN  Points to a list of abandoned SCB's.


TYPEIT,  LISTX,  SUCCEED,  FAIL,  all calls to leap are:

		 MOVE  5,control!word

The right half of the control word contains the dispatch number of
the routine to be executed.  The left half may contain one or more of
the following bits.  Ignore any other bits - leap does.

400000	This is a bracked triple search in a foreach specification
	(i.e., in the 'such that' clause)

200000	This is a GLOBAL model operation.

20000	This is a set operation in a foreach specification.

400,40,4  Attribute/Object/Value  (of A XOR O EQV V) has been bound locally
	in a foreach specification.  The argument here is the index
	into a table in the SCB containing the bound value.

200,20,2  Attribute/Object/Value is being bound by this search in a
	foreach specification.  The result, if the search succeeds,
	will be put in the SCB.

Some special routines such as NEW, and others use the left half for 
other information. The exact usage of the left half will be included
in the routine descriptions.

Below  are the (octal) dispatch numbers, all '140 of them, and
what they mean. Unless otherwise noted all routines return to the location
following the PUSHJ '17,LEAP.

The contents of ACs upon exit from leap is given.  This is subject to
change at any time.

*****	******	*****************************************************

0	FOREC	The associative searches for the foreach
		specification.  A, O, and V are in the stack in that
		order at entry.  Parts of the triple not globally
		bound are represented by table indicies.  ANY is
		represented by a zero.  An example of a foreach
		statement compilation is given later.  If the search
		fails, control is passed internally (inside of LEAP)
		to the FOREC search immediately preceding
		this one in the foreach statement.  If this is the
		first one, control goes to the fail exit (see routine
		12).  If it succeeds, it will return normally with
		the current bindings in the SCB in use.  Currently
		AC 14 will point to this SCB on exit. To determine which
		search LEAP is actually going to perform, check for
		the BINDING bits in the left half of the control word
		and the presence of ANY('0) in the stack.

		? XOR ? EQV ? As this search is not yet implemented
		this will only give an error message

1-7		RESERVED for future use.

10		10-11 are the set (list) searches in a foreach specification.
		The item, or index, and set (list) pointer are in the stack.
			A IN S

11			? IN S

12	FORGO	Start a foreach statement.  Call+2 is a JRST which is
		executed when the foreach fails.  The next cell
		(call+3) is the number of unbound variables and it
		is followed by one cell for each unbound variable
		containing the itemvar's address.  It returns
		with a pointer to the SCB in AC 14.

13	FRPOP	Put the current bindings from FOREC into core for the
		user at the end of the searches, or before a boolean
		in the foreach specification.  Unbound variables will
		get random values.

14	DOAG	This call is at the end of a foreach statement and
		returns	control internally to FOREC for the next
		group of bindings. This also saves the current values
		of the foreach locals, so that they may be restored
		to the last successful binding if future searches fail.

15	FRFALSE	Called by the FALSE result of a boolean expression
		in a foreach specification.  It is identical to
		routine 14 except that the current values of the
		locals are not saved.

16	MAKE	Make an association.  A, O, and V are in the stack
		when called.  On exit, AC 11 points to the two word
		block containing the association.

17	BMAKE	Make a bracketed triple.  A, O, V are in the stack.
		It returns the item it has associated with the triple
		on the top of the stack.

20	ERASE	Erase an assocaition.  A, O, V are in
		the stack when called.  The search routines are used.

21-27		RESERVED for future use.

30	ISTRIPLE ISTRIPLE test.  The item is in the stack when called.
		Answer returned in AC 1. (-1 TRUE, 0 FALSE).

31	SELECTOR  31-33 select a part of a bracketed triple.  The item
		associated with the triple is in the stack.


33			THIRD

34	CORPOP  inverse of routine 12. Not currently used in
		compiled code.

35	LD1	35-37 generate derived sets inside foreach specifica-
		tions. 	The two items are in the stack.  It leaves
		the a dummy item containing the next element of the
		set at the top of the stack.  (A XOR O)

36	LD2		(A'V)
37	LD3		(O EQV V) 

40	D1	40-42 generate normal derived set.  Same arguments as
		35-37. All leave a temporary set descriptor on top
		of the stack. (A XOR O)

41	D2		(A'V)

42	D3		(O=V)  

43	DELETE	Delete the item in the stack.

44	NEW	A new item with no datum is put on the top of the
		stack. Left half of control word contains type code of
		new item (1) and global bit if a global NEW.

45	NEWART	A new item with the arithmetic value in the stack as
		its is put on the top of the stack. The type code of the
		new item is contained in the left half of the control
		word. Left half contains global bit ('200000) if a 
		global NEW. NOTE if a new string item then the value
		is on top of the string stack not the arithmetic stack.

46	NEWARY	A new item with a copy of the array whose descriptor
		is in the stack as its datum is put on the top of the
		stack. Type code and global bit in left half of control

47	FDON	Release the current foreach statement for DONE or GO
		TO jumping out of foreach.

50	PUTIN	PUT the item in the stack into the set pointed to by
		AC 14 on entry and exit.

51	REMOV	REMOVE the item in the stack from the set pointed to
		by AC 14 on entry and exit.

52	SIP	For making up sets from lists of items {A,B,C,D⎇.
		The next item to insert is on the top of the stack.
		The set being built is next in the stack and is
		left on the top of the stack.

53	LSTIN	Test if the item on the top of the stack is in the list
		which is next in the stack.

54	COUNT	Returns in AC 1 the length of the set or list on the top of
		the stack.(Often compiled in-line).

55	UNIT	Returns on top of stack the first item of the set or list on
		the top of the stack at entry  (COP)

56	UNION	The union of the two sets in the stack is left on the
		top of the stack.

57 	INTER	The intersection of the two sets in the stack is 
		left on the top of the stack.

60	SUBTRA	Set subtraction left on top of the stack.  The subtra-
		hend is on top of stack at entry, other set below it.

61	STORITM	Store the set or item on the top of the stack in the
		cell pointed to by ac 14, which has a -1 in the left
		half if storing a set.  If the thing is an item you
		should never get this call since the compiler now
		generates a 'POP' in line.  If it stored a set, it
		reclaimed the old set, if any.

62		Same as 61 but also leaves the thing on the top of the

63	STIN    Test if the item on the top of the stack in in the set
		which is next in the stack.

64	POPSET	Same as 61 but puts a set in AC1.

65	SETEST	65-72 are set relationals. Both sets are in the stack

66			A>B

67			A=B

70			A NEQ B

71			A LEQ B

72			A GEQ B

73	ISIT	Test for the existance of an association
		using the search routines.  The three items are in
		the stack.

74-102  RESERVED for future use.

103	BRITM	Retrieve a bracketed triple, given A, O, V
		in the stack and put its item on the top of the stack.

104-112	RESERVED for future use

113	ITMRY	Initialize the array item on the top of the stack
		unless the global bit is set.  Then, if bit 1 is
		also on in the control word it is a global array
		item; otherwise it is just a global array with
		nothing in the stack.

114	ITMYR	Initialize a compiled in array item.You shouldn't see this
		as all array items are now dynamically allocated.

115	STLOP	Apply LOP to the set or list in AC 14 and put the item on the
		top of the stack.

116	BNDTRP	Associative boolean of form BIND x XOR BIND y EQV BIND z
		where any of the BINDs may be omitted.

117	SETCOP	Copy the set in AC 14 for use as a value parameter to
		a procedure.  New set put into loc. pointed to by AC 14.

120	SETRCL	Reclaim the set pointed to by AC 14 which was created by 117.

121  CATLST	concatenate the list on the top of the stack to
		the list below it on the stack. Return result on
		top of stack.

122  PUTAFT	searches the list pointed to by AC 14 for the item(1)
		on the top of the stack and places the item(2) below it
		on the stack inside the list after the first instance of
		item(1) or at the end of the list if item(1) is not present.

123  PUTBEF	searches the list pointed to by AC 14 for the item(1)
		on the top of the stack and places the item(2) below it
		on the stack inside the list before the first instance of 
		item(1) or at the head of the list if item(1) is not present.

124  SELFET	index on top of stack, list below index on stack. Fetches
		the n th (index) element of the list and leaves it on the

125  TSBLST	preforms the sublist operation LIST[I TO J]. J on top of stack
		I below that and list below I. Returns sublist on top of stack.

126  FSBLST	same as 125 except preforms FOR sublisting operation.

127  SETLXT	takes the list on the top of the stack and returns a set
		containing the same elements on the top of stack.

130  RPLAC	preforms LIST[N]← it. AC 14 points to LIST. it on top of 
		stack, N immediately below it.

131  REMX	performs REMOVE n FROM list. list pointed at by AC 14,
		n on top of stack.

132  REMALL     performs REMOVE ALL it FROM LIST. LIST pointed to by AC 14,
		it on top of stack.

133  PUTXA	performs PUT it IN LIST AFTER n. LIST pointed to by AC 14,
		n on top of stack, it immediately below n.

134  PUTXB      same as 133 except BEFORE.

135  LSTMAK     same as 52 except makes list

136  CALMP	call a matching procedure. on stack is a zero followed by
		parameters to matching procedure with the procedure descriptor
		at the top of the stack.

137  STK4VL	stack a ? local. On top of stack is XWD routine!increment,,satis. no.
		If satisfier unbound adds routine!increment to INDEX4 of SCB
		which is used as added to dispatch in FOREC.

140  STK4LC	stack a ? local as a matching procedure ? parameter.


Below is the actual code generated (on JULY  6,1974) by the
following statement:


A,B are declared items. X, Y, Z are itemvars.

The parts of the statement are enclosed in {⎇ in the listing.
Notice  that, in the comments below, when control is transfered to L2
or L4, it is transfered inside leap  to  the  code  called  by  those
calls.  Breakpoints at those locations would not win. In general
it is a bad idea to set breakpoints inside the associative context
as RAID and DDT get very confused by LEAP's non-standard return mechanism.
It is best to limit breakpoints to spots such as L0, L7, L8, where
everything is relatively stable.


	MOVEI	14,SCB...
	MOVEI	14,L1
	MOVEI	5,12
	X				;LOCAL 1
	Y				;LOCAL 2


L2:	PUSH	17,[A]
	PUSH	17,[B]

{(DATUM(X)=1 AND ⎇

	MOVE	2,(2)			;DATUM(X)
	CAIN	2,1
	JRST	L4			


	PUSH	P,[0]			;ANY


{(X NEQ Y) AND ⎇
{DO Z←X⎇

If you want to know what leap is doing internally during all
this, read on, and on, and on.
4. SETS and LISTS

	Sets and lists are composed of one word blocks linked as follows:

NAME:	XWD number of elements, WD2	The set or list descriptor
WD3:	XWD item number,WD4
WD4:	...
	XWD item number,WDn
WDn:	XWD item number,0

NAME: |Length  |   .    |
	    ------|---       |    .    |   WD2
	    |     ----------------|-----
            |                     |
	    |        --------------
            |        ↓
            |     ----------------------
	    |     | item no. |    .    |   WD3
            |     ----------------|-----
            |			  |
            |	     --------------
            |        ↓

	    .	  .
	    .     .
	    .	  .
            |     | item no. |    .    |
            |     ----------------|-----
            |                     |
            |        --------------
            |        ↓
            |     ----------------------
            -----→| item no. |    0    |  WDn

	The words come from the one word  free  list  (FP1)  and  are
returned  there  when  the  set or is deleted.  With sets, the items
are ordered by item number, with the lowest first.  This  means  that
the  earliest declared  or  created item will be first for local items
and the most recent for global items, whose numbers start at 4096 and
come down. The order for lists is completely program dependant.

	There  are  two  kinds of sets, permanent and temporary.  The
former are created by "PUT X IN SET1" or by assigning a set to a  set
variable.  They  stick around until deleted by the program by storing
PHI or another set into the variable.  PHI, the null  set,  causes  a
zero  to be stored into the set variable.  Temporary sets are created
by all other set operations and are indicated by a negative count  in
the first word.  For example, if you have the statement:


then A INTER B generates a temporary set, {A1,A2⎇ generates a second  one,
the  union  generates  a  third  and  deletes  the first two, and the
inclusion test deletes the third one.  If the statement is  inside  a
loop,  this happens every time.  You should assign the set expression
to a variable, if possible, to make it  permanent.   Sets  passed  by
value  to subroutines are copied, only if they are permanent, and the
copy, which looks like a permanent set, is deleted upon exit from the
procedure.   Temporary sets should be pointed to only by accumulators
and the stack; they should never be stored in variables.

	There are similarly two kinds of lists, permanent and temporary
which behave much as the corresponding kind of set.


	Describing the way associations are stored can be  done  only
with some difficulty.  We will start with some definitions to save me
writing (remember these for section 6 also).   WD1 is the first  word
of  a two word association block.  WD2 is the second word.  LH is the
left half of the word specified.  RH is the right half.  A, O, and  V
refer to the three items of an association (A XOR O EQV V).

	To start the description we look at INFOTAB (from Section 1),
an  array  which  has  an  entry for each item, both local and global
items in the case of a lower segment, indexed  by  the  item  number.
The LH of each entry contains the start of the value list [VL], which
links together all associations with this item as V.   It  points  to
WD1  of the association.  In fact, all pointers to associations point
to WD1.  The RH of each entry contains a 12 bit filed for PROPS, and
a 6 bit field for the type whose value is
returned by TYPEIT. Two byte pointers exist called PROPS and INFTB
which correspond to these fields. Simply load AC 3 with the item number
and the do a LDB ac,INFTB and ac will now magically contain the type
code.There are two similar byte pointers GPROPS and GINFTB for the
global model.

	Associations  are  stored as two word blocks in a bucket hash table.
To get the table index of the bucket we perform an operation called hashing.
There  are  many  ways  of  doing  this  but  here we hash A and O by
shifting A left one bit, exclusive ORing O into it,  and  ANDing  the
result  with  a  mask to truncate the result to the size of the table.
The contents of this bucket is a pointer to the first of a list
of things which hash to the same value (known as the conflict list).

	We  may  have several  associations  with  the same A and O,
but different V's (there is of course only a single copy of any association
so we never have the case of two associations in the store containing
the exact same A, O, and V). This  is  called  multiple  hits.

	First let us consider the easy case where there are no multiple
hits and there are no two associations which hash to the same bucket.

	0                18                35   
	*                *                  *	TYPE 1
	*  VL POINTER    *         0        *
        *                *                  *
	*           *           *           *
	*   A       *     O     *     V     *
	*           *           *           *
	0           12          24         35

	The  association  fits  in  one  word  since the maximum item
number is twelve bits long.   The  VL  pointer  points  to  the  next
association  on  the  value list for V or is zero if this is the last
	If  there  are multiple hits, then the entry on the conflict
list looks like this:

	0                18                35   
	*                *                  *	TYPE 2
	*  MH POINTER    *         0        *
        *                *                  *
	*           *           *           *
	*   A       *     O     *     0     *
	*           *           *           *
	0           12          24         35

	The  zero  in the V part of WD2 indicates multiple hits [MH].
This block is not an association, it is the header block for  a  list
of associations with this A and O.  The LH of WD1 points to the first
association on the list, all of which [type 3] are the same as type 1
except  that  the  RH of WD1 points to the next association on the MH
list, or is zero for the last one. The blocks for associations on the
MH  list  are taken from the two word free storage list (FP2) and are
returned there if the association is erased.

	If  there  are  conflicts,  the  RH  of WD1 each element of th
conflict list, which is a block of either type 1 or 2, points  to the
next association  on the conflict list [CL], which may be of either type 1
or 2, depending on whether or not there are multiple hits for that  A
and  O.   The  conflict  list  continues through the RH of WD1 of all
associations which hash to this index, with a zero for the last  one.
This   structure   is   expanded  and  collapsed  as  necessary  when
associations are made and erased. Note that when a multiple hit list
contains only two associations and one is then erased, we do not
erase the multiple hit list header but wait until there are no
associations with that A, O pair.

	For  those  who  prefer pictures with lots of spaghetti, this
mess can be represented by the picture below,  showing  the  multiple
hit  list [ML] and the conflict list [CL] for this hash table entry,
and part of one of the value lists [VL] linking into it.

INFOTAB table+V1        				    ↑
	      ↓						    VL
	      VL					    ↑
	      ↓						    ↑
hash table    ↓						    ↑
    +index:   →A1-O1-V1 →→CL→→ A2-O2-0 →→CL→→ A3-O3-0 →→CL→→ A4-O4-V1
	      ↓         ↓              ↓                    ↑
	      ↓         ML             ML                   ↑
	      ↓		↓              ↓                    ↑
	      ↓         A2-O2-V2       A3-O3-V3		    ↑
	      ↓		↓	       ↓		    ↑
	      ↓         ML             ML		    ↑
	      ↓		↓	       ↓		    ↑
	      VL        A2-O2-V5       A3-O3-V7		    VL
	      ↓         ↓	       			    ↑
	      ↓		ML    ↑→→→→→→→→→→→→→→→VL→→→→→→→→→→→→↑
	      ↓		↓     ↑
	      ↓		A2-O2-V1
	      ↓		      ↑

	If  you  do not understand the above description and picture,
you are welcome to read the code.

	Before  leaving  this  facinating  subject, there is one more
complication, which I left until last so I would not have to  include
it in the above picture.

	When a bracketed triple is created, a normal  association  is
made and linked into the hash table.  The high order bit of the LH of
WD1 is complemented from its normal value (it is now 1 for a lower
segment association and 0 for an global association) to indicate a
bracketed triple.  The next thing  in
the  value  list through the association is a one (1) word block with
the value list pointer in the LH  and  the  RH  containing  the  item
representing  the  bracketed  triple.  The  RH of the item's entry in
DATAB points to the original association block.

	To  do  fast  associative  searches, two more hash tables are
needed, one hashing O and V, with an attribute list (corresponding to
the  value  list for this hash table), and the other hashing A and V,
with an object list. Then, given two items, hashing into  the  proper
table  gives  all possible third items, and, given one item, the list
for that item given all  possible  pairs  of  items  in  the  current
associations.   Since we only have one table and list, mainly to save
core, some searches are slower than others, as hinted at  in  section
2. The associative searches are done like this:

A XOR O EQV ?	hash A and O to get a triple, or a set  of  them (the multi-
	ple hit list).
A XOR O EQV V	hash  A and O  to get V, searching the multiple hit  list if
	necessary.  There is only one possible match.
? XOR O EQV V and A XOR ? EQV V    search  Vs  value list  for all instances of the
	given A or O.
? XOR ? EQV V	Vs value list is the set of associations requested.
? XOR O EQV ? and A XOR ? EQV ?   Try using all possible A's(O's)and then use the
	A XOR O EQV ? search for each possible A (O).


	Foreach statements use the structures described in  the  last
two sections and retrieve from them items which fit the conditions of
the foreach specification.  This section describes the foreach search
control blocks (SCBs) which enable the leap routines to keep track of
the status of each search for when it is necessary  to  continue  it.
Each  foreach  statement  generates  a  new SCB when first called and
releases it when the statement is  exited.  Each SCB is  87  words  long
and contains the following:

WD1	push down pointer to the top of the stack for this block, which
	starts at WD16. The PDL initially points to WD17.

WD2	if you load AC 3 with the index of an unbound variable and
	execute WD2, you get the current satisfier in AC 1 from the
	table at WD6.

WD3	Same as WD2 except satisfier appears in AC2.

WD4	DPB X,WD4 stores the item in AC X in the table as the satisfier
	for the variable whose index is in AC 3.

WD5	minus the number of unbound variables as obtained from the
	second word after the call of leap routine 11.

WD6-WD15   a 10 word table of satisfiers.  The LH of each word is the
	current item.  The RH is the address of the itemvar the satis-
	fier is bound to.  These are filled by the search routines and
	are stored in your program by routine 12.

WD16	start of a two word dummy SCB entry below the start of the
	stack.  It contains XWD 0,-1 which stops searches in this
	block when the routines try to use it as an index into a
	table of search routines.

WD17	the JRST for the failure exit for this foreach statement.

WD18-WD86  The rest of the SCB is used as a pushdown stack containing
	one 8 word SCB entry for each active search for a triple or
	set inclusion specification in the associative context of this
	foreach statement (i.e., one is set up by the initial call,
	for each foreach statement, of routines 0-10).  The PDL
	pointer in WD1 points to the end of the SCB entry currently
	being used in a search.

	The 8 word SCB entry looks like this:

WD1	satisfier index, if unbound, or item number for the value
	of this association.

WD2	satisfier index or item number, for object of associaton
	if search routine 0-6, or the set descriptor for routines

WD3	index or item number for attribute of association, or for
	set test.

WD4	compare mask for associative searches.  It contains ones in
	the parts of the word containing bound portions of the
	triple and zeros in the remainder.

WD5	-1 if no search yet (WD6 not set up), else GEQ 0

WD6	pointer into set or associative structures (ML or VL lists)
	where search is to continue.  If it is zero search will
	fail if called again.

WD7	control word from call to this search from program, so we
	can branch back internally when a search fails.  The left
	half contains the bits and the right half contains the
	search routine to be executed (actually a number 0-10 which
	corresponds to the leap routines with those numbers).

WD8	return address from the call to this search, for when we

WD87 OF SCB -address of SCB... variable and the SCB of the dynamically
	enclosing foreach.


	Most  of  the  leap  runtime  error  messages  are  easy   to
understand. However here is the explanation for all the ones at present

<INCORRECT ITEM # FOR GLOBAL DATUM> - you have attempted to take the
	global datum of a non-global item

<LEAP SHOULD HAVE BEEN INITIALIZED> - the LEAP runtime environment has
	not been initialized properly. Theoretically you can only get this
	message if you call LEAP directly from an assembly language program

<DRYROT-LEAP:ROUTABLE> - the routine index you have given to LEAP is not
	valid. This is usually caused by having an incompatibility between
	the version of the compiler and the runtimes. Recompile, reload
	and try again.

<ASSOCIATIVE SEARCH WITH NOTHING BOUND> - you have specified a search (or erase)
	with none of the positions bound. As this particular search has 
	not yet been implemented, you lose.

<GLOBAL SEARCH WITH LOCAL ITEM> - one of the elements to a global search(or erase)
	was a local item

<MAKE WITH UNBOUND ITEM> - an argument to a MAKE statement was either the item
	BINDIT or the item ANY. As all itemvars are initialzed at load time with
	ANY this is a common error.

<GLOBAL MAKE WITH LOCAL ITEM> - one of the arguments to a global make statement
	was a local item

<DRYROT -- ERASE1>- While attempting to erase an association, it was noted
	that the association was not on the appropriate value list. Report this
	to your local LEAP expert.

<DRYROT -BRACKET CONFUSION> - while erasing a bracketed triple association,
	erase blew up. Report to LEAP expert.

<DRYROT -- ERASE2> - while erasing an association it was noted that the association
	was not on the appropriate conflict list.

<DRYROT -- ERASE3> - the association which was being erased was not on the appropriate
	multiple hit list

<NOT A BRACKETED TRIPLE>- the argrument to FIRST, SECOND, or THIRD was not
	a bracketed triple
<LOCAL DELETE OF GLOBAL ITEM>- a local delete of a global item. The delete should
	have been a global delete.

<GLOBAL DELETE OF LOCAL ITEM> - a global delete of a local item. The delete should
	have been simply delete, not global delete.

<DELETE - DELETED NON-EXISTANT ITEM> - the argument to delete was never allocated
	or had already been deleted.

<DRYROT-BRACKETED TRIPLE DELETE> - while deleting a bracketed triple item, the
	pointer to its association was found to be invalid. Report to your LEAP

<DRYROT - ITEM TYPE CONFUSION> - while deleting an item, it was found that
	the type of the item was not a valid type. Report to your LEAP expert.

<DRYROT - DELETE MISSING ARRAY ITEM> -when deleting an array item, the pointer
	to the array datum was not valid. This can occur if you have inadvertently
	assigned something  to the datum.

<STRING ARRAY ITEM CONFUSION>  - a string array item when deleted was not found
	on the appropriate string garbage collector list.

<DRYROT-TEMP. CONTAINED IN ITEM LIST OR SET > - the set or list stored in a
	set or list item now being deleted is not a valid set. This can be
	caused by assigning a not set or list datum to the datum of a set or list

<GLOBALS OVERFLOWED INTO LOCALS> - while attempting to execute a global NEW it was
	found that there were no more global items.

<LOCALS OVERFLOWED INTO GLOBALS> - while executing a local NEW it was found that
	there were no more local items.

<ITEM SPACE EXHAUSTED> - you have run out of local items. You should REQUIRE 
	more NEW!ITEMS.

<PROC EXIT WITH TEMP SET> - while releasing a value set parameter, it was found
	that the set it contained was invalid. Report to your local LEAP hacker.

<LIST SELECTOR OUT OF RANGE> - the index of list[index] was either less than 1 or
	greater than the length of the list.

<INVALID "FOR" INDEX IN SUBLIST> - the FOR index of a list sublist operation was
	found to be < 0

<INDEX FOR SUBLISTING LEQ 0- the initial index of a sublist opeation was LEQ 0
	was longer than the amount remaining in the list.

<REPLACE - INDEX LEQ 0> - in a statement of form list[index] ←  ; index was LEQ 0

<REPLACE - INDEX TOO HIGH> - in a statement of form list[index] ← index was
	greater than the length of the list.

<REMOVE - INDEX LEQ 0> - in a statement of form REMOVE n FROM list, n was LEQ 0

<REMOVE - INDEX GTR LENGTH> - in REMOVE n FROM list, n was > length(list)

<PUT- BAD INDEX> - in a PUT itm IN list AFTER(BEFORE) n. If AFTER then
	n was greater than length of list or < 0. If BEFORE then
	n was LEQ 0 or greater than the length of the list.

<ARRAY TEMP SET -CONFUSION> - while releasing an array, it was noticed that
	one of the sets or lists was invalid. Can occur if was set array item
	and was inadvertently used as a non-set array item

	non-existant item (either, deleted , or never allocated) a printname.

<ERROR - name  USED AS PNAME FOR TWO DIFFERENT ITEMS> - an attempt has been
	made to use "name" as the printname for two distinct items.

<ERROR - NULL PNAME> - the null string is an illegal pname and thus may
	not be the second argument to NEW!PNAME.

<DRYROT- PNAMES DELETE> - a SAIL error has occurred while deleting a PNAME.
	See your local SAIL hacker.

<CAN'T GET LEAP CORE> - your program has exceeded available memory and can
	not get any more core.