00100		USING MLISP2
00200	
00300	MLISP2 has most of the facilities of MLISP.  It does NOT have DEFINE,
00400	vector operations, MTRANS, and certain other special features of MLISP.
00500	MLISP2 does offer backtracking.
00600	
00700	A special version of MLISP2 is available for this class to solve the
00800	two towers problem.  Here is how to use it.
00900	
01000	(1) Prepare a file TOWER on your disk area.  It should have the
01100	declarations of two functions, TOWER and TWOTOWERS.  It may also have
01200	other function declarations and "Initiallize" Statements (see
01300	below).  The last line of the file should have the word:
01400		_EOF_
01500	The functions should NOT be within a block, as they are in MLISP.
01600	
01700	NOTE: If you are on a teletype, SOS recognizes the following
01800		equivalents:
01900			_	?9
02000			{	?[
02100			}	?]
02200	
02300	INITIALLIZE STATEMENT
02400	Assignment statements (SETQ) in MLISP2 are undone during
02500	backtracking.  Furthermore, assignment statements standing alone
02600	in your file TOWER will be undone as soon as they are done.  To
02700	make an irreversible assignment, use the Initiallize statement:
02800	
02900		X{NIL} ← <2, 3, 4> ;
03000	
03100	This sets X to the list (2 3 4).
03200	
03300	Sample file TOWER (the functions are entirely erroneous):
03400	
03500	- - - - - - - - - - - - - - - - - - - - - - - - - - - - -
03600	
03700	
03800	
03900	
04000	EXPR TOWER(N) ; <IF N ≤ 5 THEN CHOICE(N) ELSE FAILURE()> ;
04100	
04200	EXPR TWOTOWERS(N, M) ;
04300		ASSOC('ROSES, FOO) CONS MAPCAR(TOWER(N), TOWER(M)) ;
04400	
04500	FOO{NIL} ← '((ROSES RED) (VIOLETS BLUE)) ;
04600	
04700	_EOF_
     

00100	(2) Imitate the conversation depicted below to test your functions.
00200	
00300	.R TOWER
00400	
00500	*(TRANSLATE)
00600	TRANSLATING FROM FILE: TOWER
00700	
00800	
00900	***** 
01000	TOWER TWOTOWERS 
01100	***** 
01200	
01300	TRANSLATION TIME:  0 MACHINE SECONDS,  0 REAL SECONDS
01400	
01500	186 STATE STACK CELLS USED
01600	23 TOKEN STACK CELLS USED
01700	
01800	YOU ARE ABOUT TO TYPE TO MLISP2, E.G.:   PROBLEM(1);
01900	
02000	
02100	***** 
02200	*PROBLEM(1);
02300	THESE ARE THE BLOCKS YOU HAVE:
02400	
02500	(1 2 4) 
02600	*** *TEST(1);
02700	(TOWER 1)  =  (1)
02800	
02900	
03000	*** *TEST(10);
03100	(TOWER 10)  =  FAILURE
03200	
03300	
03400	*** *PROBLEM(5);
03500	THESE ARE THE BLOCKS YOU HAVE:
03600	
03700	(15 14 2 5 8 11 14) 
03800	*** *TEST(20,60);
03900	(TWOTOWERS 20 60)  =  FAILURE
04000	
04100	
04200	*** *TEST();
04300	ANSWERS WILL NOT APPEAR ON THE TERMINAL.
04400	ANSWERS RECORDED FOR GRADER
04500	
04600	*** *↑C
04700	↑C
04800	
04900	.
     

00100	Here is an explanation of the various functions you may call
00200	during your test.
00300	
00400	(TRANSLATE)
00500		Translates the functions on file TOWER and executes the
00600		Initialize Statements, if any.
00700	
00800		If there are syntax errors, they will show up in one of two
00900		ways:
01000	
01100			(a) If you are lucky, "SYNTAX ERROR" will type out,
01200			    and a blown up image of the statement that
01300			    caused the error.
01400			(b) One of your functions has an extra END or
01500			    missing " or some such thing -- the effect is
01600			    that the printout will not be complete.  For
01700			    example, the names of one or more of your
01800			    functions may not print out during translation,
01900			    or you will be returned to the top level of LISP.
02000	
02100		To correct syntax errors, return to the editor.
02200	
02300		When translation is complete, TRANSLATE automatically
02400			calls (PARSE)
02500	
02600	(PARSE)
02700		This lets you type to MLISP2 instead of to LISP.
02800		When talking to MLISP2, call the function (FOO X Y) by:
02900			FOO(X, Y);
03000		To find out the value of X, type:
03100			X;
03200		To change the value of X, use an Initialize Statement:
03300			X{NIL} ← Y ;
03400		Remember that the LISP top-level loop is:
03500			(PRINT (EVAL (READ)))
03600		The MLISP2 top-level loop is:
03700			Undo(PRINT(EVAL(Translation(input))));
03800		I.E., it inputs one MLISP2 expression, translates it
03900		to LISP, EVALs it, PRINTs the result, and Undoes
04000		all "reversible" side effects since input began.
04100	
04200	"Reversible" Side Effects
04300		X ← Y ; PUT(X, Z, P) ;
04400		Function entries & exits
04500	
04600	"Irreversible" Side Effects
04700		X{NIL} ← Y ; PUTPROP(X, Z, P) ;
04800		Array stores, RPLACA, RPLACD, input, output
04900	
05000	FAILURE();
05100		This backs up to the last CHOICE(n), and Undoes
05200		"reversible" side effects on the way.
     

00100	PROBLEM(n);
00200		Where n=1, 2, 3, 4, or 5.
00300		This initiallizes BLOCKS to one of five prepared lists
00400			and makes other vital preparations for testing
00500			your functions.
00600	
00700	TEST(a);
00800		Where `a' is an integer.
00900		This calls your function TOWER(a).  If you call it
01000			yourself, strange things may happen.  TEST
01100			re-initializes BLOCKS before it calls TOWER,
01200			in case it has been changed by earlier calls.
01300		TEST prints the arguments and value of your function.
01400		If TOWER should completely fail, TEST prints FAILURE.
01500	
01600	TEST(a, b);
01700		Where `a' and `b' are integers.
01800		This calls your function TWOTOWERS(a, b) as above.
01900	
02000	TEST() ;
02100		This calls both your functions with various
02200		prepared sets of arguments.
02300	
02400		NOTE: For PROBLEM(5); TEST() will not print the
02500			results on the terminal, but instead will
02600			report them to the grader.  Do this after
02700			you have tested your functions extensively.
02800			The grader will only see the last set of
02900			results that are reported before 11:00 AM Friday.
03000	
03100		ALSO Hand in a printout of your functions if possible.
03200			If impossible, leave them on the file TOWER.
03300	
03400	π CR
03500	CONTROL-G CR
03600	bell CR
03700		Depending on what terminal you are using.
03800		This brings you back to LISP.  To return to MLISP2,
03900		do a (PARSE)
     

00100	(TRACE ...)
00200		Call it from LISP, not from MLISP2, then return to
00300		MLISP2 to test your functions.
00400	
00500	(UNTRACE ...)
00600		Same.
00700	
00800	ERRORS!
00900		MLISP2 Syntax errors will be noted and you will be
01000		given a chance to retype the statement.
01100	
01200		LISP errors will bring you to LISP.  Type
01300		π (or CONTROL-G or bell) and CR and (PARSE) and CR
01400		to get back to MLISP2.
01500	
01600	WHEN IN DOUBT
01700		Type π CR (PARSE) CR.
01800	
01900		CONTROL-C and R TOWER again (i.e., start over)
02000	
02100		Check your program.
02200	
02300		Did you forget to type ";" to MLISP2?
02400	
02500		Follow the protocall of the sample run.
02600	
02700		See your TA.
02800	
02900		If TA can't help, call Larry Tesler x4971.