RainLisp

Let Code Block

The let keyword defines a block of code in a scope or context if you will, where some variables are only visible within it.

Let’s see an example.

(let ((a 1) (b 2))
  (+ a b))

-> 3

We have easily defined two variables a and b in one line and some code that uses them. The two variables are only visible within the let expression.

Let’s see another one.

(define (get-length) 10)
(define (get-height) 22)
(define (get-breadth) 45)

(let ((x (get-length))
      (y (get-height))
      (z (get-breadth)))
  (define product (* x y z))
  (debug "The volume of the cuboid is: ")
  (debug product)
  product)

-> 9900

We define three procedures that supposedly give the dimensions of a cuboid. We then use a let expression where we call the procedures and assign the results to three variables x, y and z, representing the cuboid’s dimensions. Then, in the let body, we define yet another variable that is the product of the former three.

The expressions in the body are executed in turn. Firstly, we are using the debug primitive procedure to write a log message. The last expression gives the result of the let itself.

Like in a procedure, you can only use the define keyword at the start of the let’s body. This is because let is syntactic sugar for a procedure call. If you want to see more details about this, see the technical specification.

Now, let’s end the language basics with quotes.

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