Grim

Grim, a small interpreted and imperative language.

Syntax

Identifiers

An identifier can start with [a-z_] and then can contain any character in [a-zA-Z0-9_].

Possible statements

Below a list of supported statements with their syntax.

Variable declaration

A variable can be declared using let keyword.
A variable name must be declared with [a-zA-Z], after it, it can contain any alphanumeric character.
A declared variable must be initialized, the type is currently inferred.
Some examples:

let a = 0;
let b = 120.0;
let c = true;
let d = c && !c;
let e = "Test";

Tip

Grim is locally scoped.
A block is defined by:

• if/if-else,
• while
• function call

A block can see every variable declared in the father blocks, father blocks cannot see locally declared variables.
Variables overshadowing is currently not supported.

Variable assignment

A value is assigned simply with =.
An example:

let a = 0;
a = 1;

If-If/else

If and if-else are supported.
An example:

let a = true;
let b = false;
if a || b {
    b = true;
}
if a && !b {
    b = false;
} else {
    let c = 0.0;
}

While

While is supported.
An example:

let a = true;
let b = false;
while a || b {
    b = true;
}

Print statement

To print a variable, an expression or a string:

let a = "test";
print (a);
print ("Example");

If you want to go to a new line you can use printl.

Input statement

To input interactively a value in a variable:

let a = 0;
input(a);

Function declaration and call

A function is declared with the following syntax:

fn fun_name (arg1, arg2) -> { return arg1 + arg2; }

A function must end with an explicit return.
Calling a function without assigning the return value means that the value is discarded after call.
A function can be called simply by:

let a = 0;
let b = 1;
let c = fun_name(a, b);
fun_name(a, b);

Pass is only by value.

Type management

To view a precise management of types compatibility see expression_evaluator.rs.
In general the only casting that can happen is int -> float if, for instance, an int is summed with a float.

Run the language

You need Rust and Cargo installed.
First you will have to build the project with:

cargo build

To run, while in the terminal:

cargo run -- path_to_grim_script

Customize the language

You can add features to the language:

1. Define the tokens into lexer.rs,
2. Define the grammar rules (BNF grammar) using tokens into grammar.lalrpop,
3. Define the interpreter rules into interpreter.rs.

Eventually you may want to add more arithmetical/logic operators, to do so you have to edit expression_evaluator.rs.

Next steps

Future features:

• Lambda functions
• REPL
• Fancier error messages