mwarzynski / uw_dust

Interpreter for Dummy Rust programming language.

Dust

D(ummy R)ust

My language is designed to be similar to Rust. Grammar (lang_grammar.cf) is based on C-- rules from BNF tutorial.

NOTE: Example files examples/good/requirementsfor* should be helpful. ;)

Types

Supported types:

• int (integer)
• float (float)
• str (string)
• bool (boolean)

Example of string usage:

text:str = "some text";
print(text); // print text to stdout

Arithmetic, comparison

Basic arithmetic, comparisons:

• +
• -
• *
• /
• <
• >
• ==
• !=

Basic arithmetic operators:

• ++
• --
• +=
• -=

Also, there are two fancy three arguments comparisons:

• x < y < z
• x > y > z

If, while

For if, while require statement without parentheses. Example:

while i < 10 {
  i++;
}

Example if:

if 0 < i < 10 && 0 < j {
  return true;
} else {
  return false;
}

if a {
    ...    
} else if b {
    ...
} else {
    ...    
}

Elif is not supported.

For

for i:int = 0, i < 10, i++ {
  // do something  
}
j:int;
for j = 1, j < 10, j++ {
  // do something more    
} 

Break, continue

Inside for and while standard implementation. Outside these Keywords produce an error.

Functions

Function declaration:

fn function_name() -> int {}
fn function_name2(a:int) -> {}

Functions accept as arguments only basic types (built-in types and structs). Functions might be declared inside other functions (and then will be visible only in the local scope). Therefore nested functions declarations are allowed.

fn hello_world() -> {
    fn hello_world_better() -> {
        print("Hello, World"):    
    }
    hello_world_better();
}

Type check

Before the execution begins, language interpreter will ensure correct usage of types in provided code.

Arrays

There are three ways to declare an array:

// array's length will be determined from value
a: [int] = [1,2,3,4,5];
// array's length is 10
a: [int*10];
// array's length is 10 and all values are 1
a: [int*10] = [ 1, .. ];

You may access array values in the standard way:

a[0]; // where 0 is an index

Dicts

There is only one way to declare dict:

scores: {str -> int}; // creates new, empty dict

Setting values (for keys) and accessing them is as follows:

scores["MIM"] = 100;
scores["PW"]  = 1;

if scores["MIM"] > scores["PW"] {
  print("MIM is the best.");
} else {
  panic("Something went wrong.");
}

Struct

Structs might be initialized anywhere, but their attributes must be of built-in type (see: supported types).

Struct declaration:

struct Point {
  x: int,
  y: int
}

How to use?

p: Point;
p.x = 10;
p.y = 20;
print(distance(p));

Scope

Scopes define visibility of variables and functions. It's possible to have global as well as local variables.

Dynamic errors

If interpreter will detect any major error (like division by zero), appropiate information will be printed to stderr. In this case, interpreter will end execution immediately. Example error: you human idiot: division by zero