I want Mouse to catch on.
The Mouse interpreter is written in Turbo Pascal. Almost everything in Mouse is single-character oriented. The language is stack-based, like Forth. To add and print 3 and 5, you say:
~ Add and print 3 plus 5
3 5 + !
$
Two stacks are used, a calculation stack and an environment stack. The environment stack supports local variables during macro calls.
#Z,c.;
calls the Z macro, passing it the value of c, one of the 26 variables in the current environment. Macros are defined at the end of the program and are signaled by a $.
$Z ~ clear screen (w/ specified foreground color) macro
~ (Royal RGB)
27 !' "T"
7 48 + !'
1% 48 + !'
@
Numbers are an exception to the single character orientation in Mouse. The 27 is pushed on the calculation stack. !' is another exception to the single character rule. !' pops and prints the character whose ascii value is on the top of the stack. Double quoted strings are sent directly to the console, so a "T" follows the ESC (ascii decimal 27) as the clear screen leadin for the Royal color monitor. To get the colors right we now need to send the ascii characters for the numbers 0 thru 7 for black, blue, ... , white.
7 48 + !'
adds 7 and 48 (48 is the ascii for the character 0) and emits the character 7.
1% 48 + !'
does the same for the 1st (and only) parameter (the value of the c variable.) So 1% is the way you represent the 1st parameter in a macro. Finally, @ is the return from macro instruction.
Looping goes like this: Let's use the delay macro to illustrate.
$D ~ delay macro
1% w : ( w. ^ w. 1 - w : )
@
To delay 300 units, you'd say
#D,300;
300 gets passed and assigned to the local work variable w ( : is the assignment operator.) Loops use the left and right parentheses and the caret ( ^ ). If by the time you get to the caret a positive value is on the top of the stack, the loop continues til you get to the right parenthesis and then you start over again at the left parenthesis. (If a non-positive value is on the top of the stack when you get to the caret, you exit from the loop.) The delay code evaluates the w variable ( . is the evaluation operator) and (since it's 300, which is positive) proceeds past the caret, re-evaluates w, pushes a 1 on the stack, pops w's value and the 1, subtracts the two and loads w with 299. This do-nothing loops simply takes time.
Mouse has an IF, of course. The color change code illustrates the IF.
3 c : ~ set initial color
( ~ code intentionally omitted
c. 1 - c : ~ change color
c. 0 < [ 3 c : ] ~ reset back to initial color when appropriate
~ code intentionally omitted
)
On the Royal, 3 gives you purple, 2 red, 1 blue and 0 black. The code above will give you these four colors and then revert back to purple again. c's value and a 0 are pushed on the stack and the < operator pops these values and pushes a 1 or a 0 on the stack depending on whether c's less than or not less than 0. If the stack has a positive value on it, the bracketed ( [ ] ) code will execute, else, it'll get skipped. So ..., [ ] signals conditional code in Mouse (it is the IF.)
I/O uses ?, ?', ! and !'. We've seen !' (pop and print the ascii decimal character on the stack.) ! prints the decimal number on the stack. ? reads a decimal number onto the stack from the keyboard and ?' reads a single character from the keyboard. A ! inside a double- quoted string is special. It sends a carriage return line feed to the screen.
Peter Grogono designed Mouse. I implemented his Pascal interpreter in Turbo Pascal. I added a &filename& feature which lets Mouse programs load and then execute other Mouse programs.
"
1. BAH
2. HUM
3. BUG
Your choice " ?'
c :
c. '1 = [&BAH&]
c. '2 = [&HUM&]
c. '3 = [&BUG&]
$
An apostrophe immediately followed by a character is one more two character token in Mouse; '1 means the character 1. If the user presses a 1, the file BAH.MSE will load and then execute.
Lee Bradley, Sysop, Z-Node #12, 203 665-1100 (no longer up)
Small Computer Support (no longer in business) 24 East Cedar Street Newington, CT 06111
(860) 666-3139 (voice)
All programs that duplicate themselves follow a similar pattern. They somehow get their own source into memory, display it, and then display it again, providing on the second pass appropriate "punctuation".
Looking for a challenging programming problem for a column I started in a computer club newsletter, I found the following in Charles Wetherell's "Etudes for Programmers".
"Write a program that prints its own source".
A few additional words are given which lay down the rules. A reference is given to an article on the subject. See Reference 1.
Solutions are given in SNOBOL, LISP, FORTRAN and ALGOL in the article. Having compilers for two of these languages, I look forward to typing the solutions in and tuning them up. I found the problem difficult and was not successful when I first tried to solve it in a language called Mouse. An MBASIC solution was contributed by a member of my computer club. It was very interesting to me and ultimately helped me finally get the Mouse solution to work.
The original solution in MBASIC (MicroSoft) had a few features which bothered me. When you ran it, its screen display was so fast and the lines which got printed were often so long that it was hard to tell what was going on. Since I wanted to publish the solution in a newsletter which had narrow columns, I tried to figure out what could be done to make it shorter and "narrower". Along the way, a second program which generated needed "DATA" statements was worked on.
As I worked on this program and the Mouse solution, it became clear to me that the tricky and interesting part to this problem involves the cosmetic aspects. My first Mouse solution was a continuous stream of characters with no carriage return line feeds. Mouse doesn't care at all about these things but I do and wanted to figure out how to get the program to generate new lines if and when the source had them.
The final solution in Mouse only works now because I fixed up the interpreter itself in a couple of respects. Mouse is a stack oriented language. I had to increase the size of the calculation stack as well as tune up the way it recognized one character. The '$' serves an important role in this language. I wanted to be able to use this character as a literal as well as an end of program indicator and a macro prefix and needed to tweak the Z80 interpreter a little to teach it when it was a straight character and when it was something else.
The article mentioned above contains a solution in pseudocode which may or may not be useful or interesting to you. Some people like pseudocode, some hate it. There's usually a fair amount of work involved in turning pseudocode into a running program. Here's the pseudocode.
Listing 1. PSEUDOCODE
string = 'print ('string = ') print (open quotes)
print (string) print (close quotes) print (string)'
print ('string = ')
print (open quotes)
print (string)
print (close quotes)
print (string)
As you study the actual solutions below and try to solve it yourself in some other language, think about the code above.
Here's the solution in Mouse. Since Mouse is probably not known to you, I will discuss the solution in some detail. A full discussion of Mouse is not appropriate here. See Reference 2 below.
Listing 2. SELFGEN.MSE
#D;#S;v:2p:
(v.w:
p.1=["!"'$!'"D0!"]
(w..'|=w.1-.'|=*
[p.1=["'|'|"]
w.2-w:"!"]
p.1=["'"]
w..!'w.1-w:
w.77>^)
p.1-p:p.^)
"!@"
$S78v:
(w:w.^w.v.:
v.1+v:)v.1-
@
$D0
'#'D';'#'S';'v':'2'p':'|'|
'('v'.'w':'|'|
'p'.'1'='['"'!'"'''$'!'''"'D'0'!'"']'|'|
'('w'.'.'''|'='w'.'1'-'.'''|'='*'|'|
'['p'.'1'='['"'''|'''|'"']'|'|
'w'.'2'-'w':'"'!'"']'|'|
'p'.'1'='['"'''"']'|'|
'w'.'.'!'''w'.'1'-'w':'|'|
'w'.'7'7'>'^')'|'|
'p'.'1'-'p':'p'.'^')'|'|
'"'!'@'"'|'|
'$'S'7'8'v':'|'|
'('w':'w'.'^'w'.'v'.':'|'|
'v'.'1'+'v':')'v'.'1'-'|'|
'@
@
Here's a discussion of the Mouse solution. Mouse programs are easier to write than to read.
#D puts the entire program on the calculation stack. It invokes the $D macro which is simply a bunch of literal characters which get pushed on the stack. #S takes what's in the stack and loads it into memory, popping the stack character by character. When variables appear in Mouse programs their address in a data area is put on the stack. Here, a hard-coded address of 78 is put on the stack to start $S off. 78 = 3 times 26 and was chosen because it's big enough not to get in the way of other variables used in the program. The main program may use addresses 0 thru 25 (corresponding to the twenty-six letters of the alphabet). The macro $S may use the next 26 values.
When $S is done, the value it returns is saved in the variable v. This value is the address of the first character of the stored program. It will be needed later.
The variable p is set to 2. The source in memory will be scanned twice and p keeps track of which pass is active.
The outer loop begins with the loading of a work variable w with the address of the first character of the program. A check is made to see if it's pass 1 or 2 (p = 2 on pass 1 and = 1 on pass 2). If it's pass 2 a $D0 is printed on a new line.
Next, the inner loop checks to see if a "||" pair is about to be processed and if so a "||" is printed if it's pass 2. In general a new line is printed if a "||" is recognized. The memory pointer is decremented by 2 here as well.
If on pass 2, a "'" gets printed. Next the character addressed by w. is printed. This is the key print statement in the program. The inner loop continues til w. = 77. The pass variable p is decremented and the next pass begins.
After the two passes are complete a new line is printed and a "@" is printed.
Like many computer programs, this one was not easy to get to work. I am very pleased with it now.
The MBASIC solution was my guide to the Mouse solution. Here it is. While I write this it occurs to me that instead of using the ASCII codes which appear in the DATA statement it should be possible to use quoted text strings instead. It would make the program a lot more readable.
Listing 3. SELFGEN.BAS
1 DEF FNS$(A)=MID$(STR$(A),2,LEN(STR$(A))-1) 2 LN=14:DT$=" DATA ":READ A 3 FOR K=1 TO A:READ B:IF B<>98 THEN PRINT CHR$(B); 4 NEXT K 5 IF B<>98 THEN PRINT 6 READ A:IF A<>99 THEN 3 7 RESTORE:READ A 8 PRINT FNS$(LN) DT$ FNS$(A) CHR$(44); 9 FOR K=1 TO A:READ B:PRINT FNS$(B); 10 IF K<>A THEN PRINT CHR$(44); 11 NEXT K:PRINT:LN=LN+1 12 READ A:IF A<>99 THEN 8 13 PRINT FNS$(LN) DT$ FNS$(A) 14 DATA 21,49,32,68,69,70,32,70,78,83,36,40,65,41,61,77,73,68,36,40,83,98 15 DATA 21,84,82,36,40,65,41,44,50,44,76,69,78,40,83,84,82,36,40,65,41,98 16 DATA 4,41,45,49,41 17 DATA 21,50,32,76,78,61,49,52,58,68,84,36,61,34,32,68,65,84,65,32,34,98 18 DATA 7,58,82,69,65,68,32,65 19 DATA 21,51,32,70,79,82,32,75,61,49,32,84,79,32,65,58,82,69,65,68,32,98 20 DATA 21,66,58,73,70,32,66,60,62,57,56,32,84,72,69,78,32,80,82,73,78,98 21 DATA 10,84,32,67,72,82,36,40,66,41,59 22 DATA 8,52,32,78,69,88,84,32,75 23 DATA 21,53,32,73,70,32,66,60,62,57,56,32,84,72,69,78,32,80,82,73,78,98 24 DATA 1,84 25 DATA 21,54,32,82,69,65,68,32,65,58,73,70,32,65,60,62,57,57,32,84,72,98 26 DATA 4,69,78,32,51 27 DATA 16,55,32,82,69,83,84,79,82,69,58,82,69,65,68,32,65 28 DATA 21,56,32,80,82,73,78,84,32,70,78,83,36,40,76,78,41,32,68,84,36,98 29 DATA 18,32,70,78,83,36,40,65,41,32,67,72,82,36,40,52,52,41,59 30 DATA 21,57,32,70,79,82,32,75,61,49,32,84,79,32,65,58,82,69,65,68,32,98 31 DATA 16,66,58,80,82,73,78,84,32,70,78,83,36,40,66,41,59 32 DATA 21,49,48,32,73,70,32,75,60,62,65,32,84,72,69,78,32,80,82,73,78,98 33 DATA 11,84,32,67,72,82,36,40,52,52,41,59 34 DATA 21,49,49,32,78,69,88,84,32,75,58,80,82,73,78,84,58,76,78,61,76,98 35 DATA 3,78,43,49 36 DATA 21,49,50,32,82,69,65,68,32,65,58,73,70,32,65,60,62,57,57,32,84,98 37 DATA 5,72,69,78,32,56 38 DATA 21,49,51,32,80,82,73,78,84,32,70,78,83,36,40,76,78,41,32,68,84,98 39 DATA 9,36,32,70,78,83,36,40,65,41 40 DATA 99
Reference 1. "Etudes for Programmers", Charles Wetherell, Prentice- Hall Inc., 1978.
Reference 2. "Mouse, a language for microcomputers", Peter Grogono, Petrocelli Books Inc., 1983.
Last updated on 6/22/86, Lee Bradley