A Virtual machine and Compiler for PL/0 language programming language. The language allows you to evaluate expressions, call procedures, provide arguments for procedures, capture return value of procedures, read input, and output evaluated expressions.
The compiler compiles PL/0 source code into machine code, which when loaded on the Virtual Machine, runs as syntactically expected. For example:
var n;
procedure fact(n);
begin
if n < 0 then return -1;
if n < 2 then return 1;
return fact(n - 1) * n;
end;
procedure abs(n);
begin
if n < 0 then return -n;
return n;
end;
begin
read n;
write fact(abs(n)) + 5 + fact(fact(n * (2 / 2)));
end.Given an input of 3, the output of this program (.\pvm.exe a.plmc) is:
$ ./pvm.exe a.plmc
PL/0 VM:
Input integer = 3
// 3! + 5 + ((3 * (2/2))!)!
// 6 + 5 + ((3 * 1)!)!
// 11 + (6)!
// 11 + 720
PL/0 VM: 731 // = 731// Base
(1) program := block ".".
(2) block := { constdec | vardec | procdec } statement.
// Declarations
(3) constdec := "const" ident "=" number {"," ident "=" number } ";".
(4) vardec := "var" ident {"," ident } ";".
(5) procdec := procedure ident "(" [ ident {"," ident}] ");" block ";".
// Statements
(6) statement := [
ident ":=" expression
| [ "call" ] ident "(" [ expression {"," expression } ");"
| "begin" { statement ";" } "end"
| "if" condition "then" statement [ ";" "else" statement ]
| "while" condition "do" statement
| "read" ident
| "write" expression
| "return expression
| ε
] .
// Conditions and expressions
(7) condition := "odd" expression
| expression rel-op expression.
(8) rel-op := "=" | "<>" | "<" | ">" | "<=" | ">=".
(9) expression := ["+" | "-"] term { ("+" | "-") term }.
(10) term := factor { ("*" | "/" ) factor }.
(11) factor := ident | number | "(" expression ")".
(12) number := digit { digit }.
(13) ident := letter { letter | digit }
(14) digit := "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9".
(15) letter := "a" | "b" | ... | "y" | "z" | "A" | "B" | ... | "Y" | "Z".
// NOTE:
// [] Means optional items
// {} Means repeat 0 or more times
// A period . indacates the end of a defintion of a syntactic class
Implemented in C, the stack machine has two memory stores:
- The stack, which contains data to be used by the PM/0 CPU.
- The Code (or "text"), which contains instructions for the VM.
It has five registers to handle the stack and the code/text segments.
- BP - Base Pointer
- SP - Stack Pointer
- PC - Program Counter
- IR - Instruction Register (implemented as pointer to the instruction in memeory)
- RP - Register Pointer (Keeps track of the base of the register)
This machine also has a Register File (RF) with eight (20) registers (changeable in pvm.h).
To run the PL/0 VM you must first compile the PVM's source code to produce an executable.
NOTE that we must link C's math library by using the -lm directive.
gcc -lm -g pvm.c -o pvm.exe
Once the code is compiled you are able to run the VM provided a machine code [INPUT_FILE] as follows:
./pvm.exe [INPUT_FILE]
Furthermore, the Virtual Machine supports the following Directives:
-a ./pvm.exe [INPUT_FILE] -a prints the Decoded Instructions Set
-v ./pvm.exe [INPUT_FILE] -v prints the VM State on each cycle
-i ./pvm.exe [INPUT_FILE] -i The VM State if printed, will be printed with indicators
Both of these Directives write to stdout, so it's possible to direct the output to using the output redirection operator ( > ).
To write both the Decoded Instructions Set and the VM State to vmlog.txt, for example.
./pvm.exe [INPUT_FILE] -v -a >vmlog.txt
Note that you can change vmlog.txt to any filepath you wish.
Compile the source code with the following:
gcc -lm -g pvm.c -o pvm.exe
Afterwards, run the program with the following line:
valgrind --leak-check=full ./pvm.exe [INPUT_FILE]
Each instruction contains four components:
(1) OP - The operation cod
(2) R - Refers to a register
(3) L - The lexicographical level or a register in arithmetic and relational instructions
(4) M - Depending on the operation, it indicates a constant, program address, data address, or a register.
(1) lit LIT - R, 0, M - Loads a constant value (literal) M into Register R
(2) rtn RTN 0, 0, 0 - Returns from a subroutine and restore the caller environment
(3) lod LOD R, L, M - Load value into a selected register from the stack location at offset M from Llexicographical levels down
(4) sto STO - - Store value from a selected register in the stack location at offset M from L lexicographicallevels down
(5) cal CAL - 0, L, M - Call procedure at code index M
(6) inc INC - 0, 0, M - Allocate M locals (increment sp by M). First four are Functional Value, StaticLink (SL), Dynamic Link (DL), and Return Address (RA)
(7) jmp JMP - 0, 0, M - Jump to instruction M
(8) jpc JPC - R, 0, M - Jump to instruction M if R = 0
(9) out SIO - R, 0, 1 - Write a register to the screen
(10) rin SIO - R, 0, 2 - Read in input from the user and store it in a register
(11) ext SIO - 0, 0, 3 - End of program (program stops running)
(12) neg - NEG - Reg[R] = -Reg[R]
(13) add - ADD - Reg[R] = Reg[L] + Reg[M]
(14) sub - SUB - Reg[R] = Reg[L] - Reg[M]
(15) mul - MUL - Reg[R] = Reg[L] * Reg[M]
(16) div - DIV - Reg[R] = Reg[L] / Reg[M]
(17) odd - ODD - Reg[R] = Reg[L] % 2
(18) mod - MOD - Reg[R] = Reg[L] % Reg[M]
(19) eql - EQL - Reg[R] = Reg[L] == Reg[M]
(20) neq - NEQ - Reg[R] = Reg[L] != Reg[M]
(21) lss - LSS - Reg[R] = Reg[L] < Reg[M]
(22) leq - LEQ - Reg[R] = Reg[L] <= Reg[M]
(23) gtr - GTR - Reg[R] = Reg[L] > Reg[M]
(24) geq - GEQ - Reg[R] = Reg[L] <= Reg[M]
(12) reg_l - REG_L - 0, 0, M - RP += M ------------(Register Pointer M levels "deeper")
(13) reg_r - REG_R - 0, 0, 0 - RP = Reg[RP - 1] ----(Register Pointer 1 level "higher")
(14) reg_b - REG_B - R, 0, 0 - Reg[R] = RP ---------(LODs Register Pointer into Reg[R])
The PL/0 Compiler consists of a Scanner and a Parser that both run as part of the compilation process.The compiler reads PL/0 source code and converts it to machine code (an instruction set).
To run the PL/0 Compiler you must first compile the Compiler's source code to produce an executable.
NOTE that we must link C's math library by using the -lm directive.
gcc -lm -g compiler.c -o compiler.exe
Once the code is compiled you are able to run the Compiler provided a PL/0 source code [INPUT_FILE] as follows:
./compiler.exe [INPUT_FILE]
The compiler will output and explain any error that occurs during the compilation process.
$ ./compile.exe codes/while05.txt -o compiled_factorial.plmc
PL/0 COMPILER:
INTERRUPTED - Assignment operator ":=" expected (ERR 13).
LINE 15, 14: factorial = i * factorial;
^By default the compiler saves the compiled machine code to a.plmc (PLMC stands for PL/0 Machine Code).
You can configure the compiler using the following directives:
-l ./compiler.exe [INPUT_FILE] -l prints the lexeme table and list produced from the source code.
-a ./compiler.exe [INPUT_FILE] -a prints the produced Machine Code (not decoded)
-o ./compiler.exe [INPUT_FILE] -o [OUTPUT_FILE] - Directs the compiler to write the produced machine code to a specific file, which path to is [OUTPUT_FILE].
For example the Following ./compiler.exe -a factorial.plc -o factorial.plmc will compile the source code file, factorial.plc, and save the produced machine code to factorial.plmc as well as write (print) that machine code to STDIN.
Given a PL/0 source code file factorial.plc, we can compile and run it on the VM by following these steps:
NOTE: You must first compile both the PL/0 Virtual Machine and the PL/0 Compiler (instructed previously).
- Compile the source code:
./compiler.exe factorial.plc -o factorial.plmc - Run the produced machine code on the VM:
./pvm.exe factorial.plmc
The factorial.plc file:
var n;
procedure fact(n);
begin
if n < 0 then return -1; /* -1 represents an error */
if n < 2 then return 1; /* 0! = 1! = 1 */
return n * fact(n - 1); /* n * (n - 1)! */
end;
begin
read n;
write fact(n);
end.The output of running the compiled code on the Virtual Machine (input 5 from user):
$ ./pvm.exe a.plmc -a -v
PL/0 VM:
Input integer = 5
PL/0 VM: 120The produced factorial.plmc machine code:
Decoded Machine Instructions:
("factorial.plmc")
----------
Line OP R L M
0 JMP 0 0 32
1 JMP 0 0 2
2 INC 0 0 5
3 LOD 0 0 4
4 LIT 1 0 0
5 LSS 0 0 1
6 JPC 0 0 11
7 LIT 0 0 1
8 NEG 0 0 0
9 STO 0 0 0
10 RTN 0 0 0
11 LOD 0 0 4
12 LIT 1 0 2
13 LSS 0 0 1
14 JPC 0 0 18
15 LIT 0 0 1
16 STO 0 0 0
17 RTN 0 0 0
18 LOD 0 0 4
19 REG_B 2 0 0
20 REG_L 0 0 3
21 LOD 1 0 4
22 LIT 2 0 1
23 SUB 1 1 2
24 STO 1 0 9
25 CAL 0 1 1
26 REG_R 2 0 0
27 LOD 1 0 5
28 MUL 0 0 1
29 STO 0 0 0
30 RTN 0 0 0
31 RTN 0 0 0
32 INC 0 0 5
33 SIO 0 0 0
34 STO 0 0 4
35 REG_B 1 0 0
36 REG_L 0 0 2
37 LOD 0 0 4
38 STO 0 0 9
39 CAL 0 0 1
40 REG_R 1 0 0
41 LOD 0 0 5
42 SIO 0 0 0
43 SIO 0 0 3 The Virtual Machine's State (with indicators) while running the program, with input 5 from the user:
VM State Log:
------------------------
BP, SP, RP Indicators
` - Base Pointer BP
^ - Stack Pointer SP
, - Register Pointer RP
------------------------
PC BP SP REGISTERS[20]
Initial values 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack:
`^
,
0 JMP 0 0 32 32 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack:
`^
,
32 INC 0 0 5 33 1 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 0
` ^
PL/0 VM: Input integer = 5
,
33 SIO 0 0 0 34 1 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 0
` ^
,
34 STO 0 0 4 35 1 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5
` ^
,
35 REG_B 1 0 0 36 1 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5
` ^
,
36 REG_L 0 0 2 37 1 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5
` ^
,
37 LOD 0 0 4 38 1 5 5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5
` ^
,
38 STO 0 0 9 39 1 5 5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5
` ^
,
39 CAL 0 0 1 1 5 5 5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5
`^
,
1 JMP 0 0 2 2 5 5 5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5
`^
,
2 INC 0 0 5 3 5 10 5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
3 LOD 0 0 4 4 5 10 5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
4 LIT 1 0 0 5 5 10 5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
5 LSS 0 0 1 6 5 10 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
6 JPC 0 0 11 11 5 10 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
11 LOD 0 0 4 12 5 10 5 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
12 LIT 1 0 2 13 5 10 5 0 5 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
13 LSS 0 0 1 14 5 10 5 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
14 JPC 0 0 18 18 5 10 5 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
18 LOD 0 0 4 19 5 10 5 0 5 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
19 REG_B 2 0 0 20 5 10 5 0 5 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
20 REG_L 0 0 3 21 5 10 5 0 5 2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
21 LOD 1 0 4 22 5 10 5 0 5 2 2 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
22 LIT 2 0 1 23 5 10 5 0 5 2 2 0 5 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
23 SUB 1 1 2 24 5 10 5 0 5 2 2 0 4 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
24 STO 1 0 9 25 5 10 5 0 5 2 2 0 4 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
25 CAL 0 1 1 1 10 10 5 0 5 2 2 0 4 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
`^
,
1 JMP 0 0 2 2 10 10 5 0 5 2 2 0 4 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
`^
,
2 INC 0 0 5 3 10 15 5 0 5 2 2 0 4 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
3 LOD 0 0 4 4 10 15 5 0 5 2 2 4 4 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
4 LIT 1 0 0 5 10 15 5 0 5 2 2 4 0 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
5 LSS 0 0 1 6 10 15 5 0 5 2 2 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
6 JPC 0 0 11 11 10 15 5 0 5 2 2 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
11 LOD 0 0 4 12 10 15 5 0 5 2 2 4 0 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
12 LIT 1 0 2 13 10 15 5 0 5 2 2 4 2 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
13 LSS 0 0 1 14 10 15 5 0 5 2 2 0 2 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
14 JPC 0 0 18 18 10 15 5 0 5 2 2 0 2 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
18 LOD 0 0 4 19 10 15 5 0 5 2 2 4 2 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
19 REG_B 2 0 0 20 10 15 5 0 5 2 2 4 2 1 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
20 REG_L 0 0 3 21 10 15 5 0 5 2 2 4 2 5 0 0 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
21 LOD 1 0 4 22 10 15 5 0 5 2 2 4 2 5 0 4 0 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
22 LIT 2 0 1 23 10 15 5 0 5 2 2 4 2 5 0 4 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
23 SUB 1 1 2 24 10 15 5 0 5 2 2 4 2 5 0 3 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
24 STO 1 0 9 25 10 15 5 0 5 2 2 4 2 5 0 3 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
25 CAL 0 1 1 1 15 15 5 0 5 2 2 4 2 5 0 3 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
`^
,
1 JMP 0 0 2 2 15 15 5 0 5 2 2 4 2 5 0 3 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
`^
,
2 INC 0 0 5 3 15 20 5 0 5 2 2 4 2 5 0 3 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
3 LOD 0 0 4 4 15 20 5 0 5 2 2 4 2 5 3 3 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
4 LIT 1 0 0 5 15 20 5 0 5 2 2 4 2 5 3 0 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
5 LSS 0 0 1 6 15 20 5 0 5 2 2 4 2 5 0 0 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
6 JPC 0 0 11 11 15 20 5 0 5 2 2 4 2 5 0 0 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
11 LOD 0 0 4 12 15 20 5 0 5 2 2 4 2 5 3 0 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
12 LIT 1 0 2 13 15 20 5 0 5 2 2 4 2 5 3 2 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
13 LSS 0 0 1 14 15 20 5 0 5 2 2 4 2 5 0 2 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
14 JPC 0 0 18 18 15 20 5 0 5 2 2 4 2 5 0 2 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
18 LOD 0 0 4 19 15 20 5 0 5 2 2 4 2 5 3 2 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
19 REG_B 2 0 0 20 15 20 5 0 5 2 2 4 2 5 3 2 1 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
20 REG_L 0 0 3 21 15 20 5 0 5 2 2 4 2 5 3 2 8 0 0 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
21 LOD 1 0 4 22 15 20 5 0 5 2 2 4 2 5 3 2 8 0 3 0 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
22 LIT 2 0 1 23 15 20 5 0 5 2 2 4 2 5 3 2 8 0 3 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
23 SUB 1 1 2 24 15 20 5 0 5 2 2 4 2 5 3 2 8 0 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
24 STO 1 0 9 25 15 20 5 0 5 2 2 4 2 5 3 2 8 0 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
25 CAL 0 1 1 1 20 20 5 0 5 2 2 4 2 5 3 2 8 0 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
`^
,
1 JMP 0 0 2 2 20 20 5 0 5 2 2 4 2 5 3 2 8 0 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
`^
,
2 INC 0 0 5 3 20 25 5 0 5 2 2 4 2 5 3 2 8 0 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
3 LOD 0 0 4 4 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
4 LIT 1 0 0 5 20 25 5 0 5 2 2 4 2 5 3 2 8 2 0 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
5 LSS 0 0 1 6 20 25 5 0 5 2 2 4 2 5 3 2 8 0 0 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
6 JPC 0 0 11 11 20 25 5 0 5 2 2 4 2 5 3 2 8 0 0 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
11 LOD 0 0 4 12 20 25 5 0 5 2 2 4 2 5 3 2 8 2 0 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
12 LIT 1 0 2 13 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
13 LSS 0 0 1 14 20 25 5 0 5 2 2 4 2 5 3 2 8 0 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
14 JPC 0 0 18 18 20 25 5 0 5 2 2 4 2 5 3 2 8 0 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
18 LOD 0 0 4 19 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
19 REG_B 2 0 0 20 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 1 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
20 REG_L 0 0 3 21 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 0 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
21 LOD 1 0 4 22 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 2 0 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
22 LIT 2 0 1 23 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
23 SUB 1 1 2 24 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 1 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
24 STO 1 0 9 25 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 1 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
25 CAL 0 1 1 1 25 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 1 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
`^
,
1 JMP 0 0 2 2 25 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 1 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
`^
,
2 INC 0 0 5 3 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 1 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
3 LOD 0 0 4 4 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 1 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
4 LIT 1 0 0 5 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 0 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
5 LSS 0 0 1 6 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 0 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
6 JPC 0 0 11 11 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 0 0 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
11 LOD 0 0 4 12 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 0 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
12 LIT 1 0 2 13 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
13 LSS 0 0 1 14 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
14 JPC 0 0 18 15 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
15 LIT 0 0 1 16 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 0 15 20 26 1
` ^
,
16 STO 0 0 0 17 25 30 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2 | 1 15 20 26 1
` ^
,
17 RTN 0 0 0 26 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
26 REG_R 2 0 0 27 20 25 5 0 5 2 2 4 2 5 3 2 8 2 2 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
27 LOD 1 0 5 28 20 25 5 0 5 2 2 4 2 5 3 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
28 MUL 0 0 1 29 20 25 5 0 5 2 2 4 2 5 3 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 0 10 15 26 2
` ^
,
29 STO 0 0 0 30 20 25 5 0 5 2 2 4 2 5 3 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3 | 2 10 15 26 2
` ^
,
30 RTN 0 0 0 26 15 20 5 0 5 2 2 4 2 5 3 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
26 REG_R 2 0 0 27 15 20 5 0 5 2 2 4 2 5 3 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
27 LOD 1 0 5 28 15 20 5 0 5 2 2 4 2 5 3 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
28 MUL 0 0 1 29 15 20 5 0 5 2 2 4 2 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 0 5 10 26 3
` ^
,
29 STO 0 0 0 30 15 20 5 0 5 2 2 4 2 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4 | 6 5 10 26 3
` ^
,
30 RTN 0 0 0 26 10 15 5 0 5 2 2 4 2 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
26 REG_R 2 0 0 27 10 15 5 0 5 2 2 4 2 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
27 LOD 1 0 5 28 10 15 5 0 5 2 2 4 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
28 MUL 0 0 1 29 10 15 5 0 5 2 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 0 1 5 26 4
` ^
,
29 STO 0 0 0 30 10 15 5 0 5 2 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5 | 24 1 5 26 4
` ^
,
30 RTN 0 0 0 26 5 10 5 0 5 2 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
26 REG_R 2 0 0 27 5 10 5 0 5 2 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
27 LOD 1 0 5 28 5 10 5 0 5 24 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
28 MUL 0 0 1 29 5 10 5 0 120 24 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 0 1 1 40 5
` ^
,
29 STO 0 0 0 30 5 10 5 0 120 24 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5 | 120 1 1 40 5
` ^
,
30 RTN 0 0 0 40 1 5 5 0 120 24 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5
` ^
,
40 REG_R 1 0 0 41 1 5 5 0 120 24 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5
` ^
,
41 LOD 0 0 5 42 1 5 120 0 120 24 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5
` ^
,
42 SIO 0 0 0 43 1 5 120 0 120 24 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5
` ^
PL/0 VM: 120
,
43 SIO 0 0 3 44 1 5 120 0 120 24 2 24 6 5 6 2 8 2 1 11 1 2 1 0 0 0
Stack: 0 0 0 0 5
` ^There are a couple of issues with global variables and variable scopes that have to be defined and addressed.
As of now, global variables are NOT supported by the compiler. While they are acceptable, they produce undefined behavior.
Variables you wish to use in procedures must be passed as arguments.
The arguments themselves are evaluations of expressions, variable are passed by value and not by reference.
Given the following program.plc:
var n;
procedure fact(n);
begin
if n < 0 then return -1;
if n < 2 then return 1;
return fact(n - 1) * n;
end;
procedure abs(n);
begin
if n < 0 then return -n;
return n;
end;
begin
read n;
write fact(abs(n)) + 5 + fact(n);
end.This error would appear:
$ ./compiler.exe demo/prog01.plc
PL/0 COMPILER:
INTERRUPTED - redeclaration of n
LINE 10, 15: procedure abs(n);
^Changing the argument name (and preceding references) to 'k' (or any other identifier) would allow the file to compile.
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