SLC

Simple Language Compiler (OCaml)

Table of Contents

• Table of Contents
• SL
  • Grammar
  • Example 1: Factorial
  • Example 2: Syracuse
• Usage

SL

SL is a very, very, very simple language which only supports basic math, 6 variables and basic control flow. All values are parsed as 64-bit integers, and the one print statement can only print those numbers, followed by a newline.

Grammar

The grammar of the SL is very simple as well; take a look below:

variable ::= x | y | z | a | b | c
digit ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
integer ::= <digit> | <digit><integer>
atom ::= <variable> | <integer>
unary_op ::= - | !
binary_op ::= + | - | * | / | < | =
expr ::= <atom> | <unary_op><atom> | <atom><binary_op><atom>
stmt ::= 
    print <variable> | 
    <variable> := <expr> | 
    while <variable> do (<stmt-list>) | 
    if <variable> then (<stmt-list>) else (<stmt-list>)
stmt-list ::= <stmt> | <stmt>;<stmt-list>
program ::= <stmt-list>#

Note how the program has to be delimited by a # sign. Everything after is regarded as comments. See some examples below.

Example 1: Factorial

x := 5;
a := 1;
c := 0 < x;
while c do (a := a * x ; x := x - 1 ; c := 0 < x);
print a
#

This program will compute the factorial of 5 (5!) in the while loop. Once the value is computed, it is printed out.
The variables used are:

Variable	Usage
a	Accumulator for the value
c	Condition variable
x	Starting value

The output for this simple program should be:

120

Example 2: Syracuse

x := 45 ;
b := x = 1 ;
c := !b ;

while c do
    (   print x ;
        y := x / 2 ;
        z := 2 * y ;
        c := z = x ;
        if c then
            ( x := y )
        else
        (   b := x = 1 ;
            c := !b ;
            x := x * 3 ;
            x := x + 1
        )
    )
#

This slightly more complex program will compute every number in the Syracuse series of 45 and print each of them to the terminal.
Notice how the modulo-2 computation is done: the value x is divided by two and then multiplied again. If it matches with the original value, then the value is even. Otherwise, it's odd.

The variables used are:

Variable	Usage
b	Temporary variable for the conditions
c	Condition variable
x	Current value in the Syracuse series
y	Helper variable for the division/mod-2 check
z	Contains the result of the division/mod-2 check

The ouptut for this program should be

45
136
68
34
17
52
26
13
40
20
10
5
16
8
4
2
1

Usage

Note: to build SLC, you require the dune build system

slc <infile> [-comp <true/false> -out <outfile>] [-exec <true/false>] [-help] [--help]

The -comp flag (when used together with -out) will compile the code in infile to X86-64 assembly (in Intel syntax, no prefixes).
The -exec flag will run the code in infile The -help and --help flags will both print the help message.

X86-64 to machine code

Due to a bug (I think), we need another C file to help with the linking. This file should contain the following code:

#include <stdio.h>
#include <stdint.h>

void _printf(int64_t i) {
    printf("%ld\n", i);
}

This file is provided in the repository as helper.c.

When this file exists, you can just compile the X86-64 output file from SLC and compile it together with the helper file to obtain an executable.