Why LET doesn't work with VECTOR?

Question

Instead of

(let [x 1] (my-expression))

I'm trying to use:

(let (vector x 1) (my-expression))

Don't ask why, I just like normal brackets more. But Clojure says:

let requires a vector for its binding in ...

What's wrong?

Answer 1

The let special form binding form is required to be a vector literal not just an expression that would evaluate to a vector.

Why? Roughly stated, the expression must be compiled before it can be evaluated. At compile-time (vector x 1) will not have been evaluated to a vector, it will just be a list. Indeed if it were to be evaluated, the arguments of vector would be evaluated, meaning x would have to be resolved. But, you don't want x to be resolved, you want it bound.

Answer 2

let requires a vector for it's bindings (at compile time) so trying to put a vector functional call in its place won't work (as that will only produce a vector at runtime).

However you can make your own let with a bit of macro-fu:

(defmacro mylet [bindings & exprs]
  `(let ~(vec bindings) ~@exprs))

(mylet (x 1) (inc x))
=> 2