jamesroutley/sketch

Sketch

Sketch is a simple lisp interpreter, written in Go.

Install

1. Install Go
2. Run go get -u github.com/jamesroutley/sketch

You can now run the Sketch interpreter in a shell:

$ sketch

Running it without any arguments will drop you in a REPL (read, eval, print loop). Here, you can use the language interactively. For example, you can:

Perform maths calculations

user> (+ 1 1)
2

Sketch (and most other Lisps) use prefix notation, sometimes called Polish notation. Operators, such as + which adds two numbers, are written before the arguments they operate on. This might seem unusual, but what it lacks in familiarity it makes up in consistency.

Unlike other languages which use infix notation for maths (e.g. 1 + 1), there's no special syntax for maths functions. Addition just calls a function, which takes two arguments, and returns the sum of them.

Define variables

user> (def a 1)
1
user> a
1

Define your own functions

user> (defn add-1 (x) (+ x 1))
#<function>
user> (add-1 2)
3

You can also define anonymous functions with:

user> (fn (x) (+ x 1))
#<function>
user> ((fn (x) (+ x 1)) 2)
3

Because def assigns a name to a value, you can use it in conjunction with fn to create a named function:

user> (def add-1 (fn (x) (+ x 1)))
#<function>

In fact, this is exactly what defn is doing - defn is just syntactic sugar which is expanded to (def ... (fn ...)) by the interpreter before it's evaluated.