Sim: A Simple programming language based on LLVM

Sim is intended as a demostration of programming lanugage design, though it has something more than Kaleidoscope. Visitor design pattern makes it more extensiable.

Table of Content

• Build for Linux
• Code example
• Features

Build for Linux

1. Build and install LLVM, make sure LLVM library for cmake are properly installed.

2. Download source
   #git clone https://github.com/yyqgituser/sim.git
   #cd sim
   #mkdir build
   #cd build
   #cmake ..
   #make
   #sudo make install

3. Run examples, simc only compile source to object file(.o file), you need a linker to generate executable file(here we use gcc as a linker)
   #cd examples
   #simc hello.sim
   #gcc hello.o -o hello
   #./hello

Except the .o file, simc also generate file hello.ll which includes IR code.

If you want to build Sim for windows, you need install MinGW and other tools.

Code example

// proto type declarations for calling C function
int getchar();
int putchar(int c);
int printf(string s, ...);

int readInt() {
	int c = getchar();
	int v = 0;
	while (c >= 48 && c <= 57) {
		v = v * 10 + c - 48;
		c = getchar();
	}
	return v;
}

int fib(int n) {
    if (n <= 2) {
        return 1;
    }
    return fib(n - 1) + fib(n - 2);
}

int main() {
    int n = readInt();
    for (int i = 1; i <= n; i++) {
        printf("%d: %d\n", i, fib(i));
    }
    return 0;
}

More examples can be found in examples

Features

1. Static type check
   Type: int, double, string, boolean, void. int is a 32 bits signed integer and double is 64 bits. string is a zero-ended 8 bits array.

2. Grammar, refer to grammar and lex files

3. Control flow
   Support if/else, while/for just like normal C syntax.

4. Literal
   int: 123
   double: 1.23 1e10
   boolean: true false
   string: "a string\n"
   array: {1, 2, 3}

5. Expression
   Support common C-like operators: || && == != < > <= >= | & << >> + - * / % ^ ! ()
   Don't support shortcut evaluation of logic expression.
   Don't support '?' expression
   Don't support '++' and '--' as operators, but support them as statement. for example:

a = b++; // illegal
i++; // legal

Type cast are only supported between numbers, in this case, only int <-> double convertion.

6. Function
   Support user defined function. Function declaration without body is allowed, it will be treated as external function, and it rely on the linker to find and link that function into the final executable file. In this way Sim program can call some C library function.

7. Array and string
   Array type and string type variable are implemented as reference, like C Pointers.

8. Everything in stack!
   Sim don't have runtime heap, except global variables, all variables are allocated from stack.

9. Dead code detection
   Sim compiler will report error if it detected some unreachable code.

int a;
if(n == 1) {
	return 1;
} else {
	return 2;
}
a = 1; // error