Scheme beginner here. I've just read SICP which in the end doesn't teach much about Scheme itself.
I was baffled with the meta-circular evaluator so I'm beginning to read _Lisp in Small Pieces_ by Christian Queinnec.
I found this in a footnote in the first pages. I thought it was interesting and I'm sharing it here.
(let ((x π₁)) π₂) ≡ ((lambda (x) π₂) π₁)
As an example, an expression like
(let ((a 3) (b 4)) (+ a b)) would expand to
((lambda (a b) (+ a b)) 3 4)
So, the macro for the basic
let is simply
(define-syntax let (syntax-rules () ((let ((var val) ...) body ...) ((lambda (var ...) body ...) val ...))))