Lexer for the Monkey Programming Language

A lexer for the Monkey programming language as presented in the book Writing An Interpreter In Go.

Language:

Copy pasting from the book:

Here is how we bind values to names in Monkey:

let age = 1; 
let name = "Monkey"; 
let result = 10 * (20 / 2);

Besides integers, booleans and strings, the Monkey interpreter we’re going to build will also support arrays and hashes. Here’s what binding an array of integers to a name looks like:

let myArray = [1, 2, 3, 4, 5];

And here is a hash, where values are associated with keys:

let thorsten = {"name": "Thorsten", "age": 28};

Accessing the elements in arrays and hashes is done with index expressions:

myArray[0] // => 1 
thorsten["name"] // => "Thorsten"

The let statements can also be used to bind functions to names. Here’s a small function that adds two numbers:

let add = fn(a, b) { return a + b; };

But Monkey not only supports return statements. Implicit return values are also possible, which means we can leave out the return if we want to:

let add = fn(a, b) { a + b; };

And calling a function is as easy as you’d expect:

add(1, 2);

A more complex function, such as a fibonacci function that returns the Nth Fibonacci number, might look like this:

let fibonacci = fn(x) { 
    if (x == 0) { 
        0
    } else { 
        if (x == 1) {
             1 
        } else { 
             fibonacci(x - 1) + fibonacci(x - 2);
        }
    }
};

Note the recursive calls to fibonacci itself! Monkey also supports a special type of functions, called higher order functions. These are functions that take other functions as arguments. Here is an example:

let twice = fn(f, x) { return f(f(x)); }; 
let addTwo = fn(x) { return x + 2; }; 
twice(addTwo, 2); // => 6

Building:

To run the REPL, clone the repository and run:

cd lexer-go
go run main.go

The executable will be generated in the bin directory.

To run the tests:

go test ./lexer

Melkor-1/lexer-go

Lexer for the Monkey Programming Language

Language:

Building: