6.18.1.2 Comments

Comments in Scheme source files are written by starting them with a semicolon character (;). The comment then reaches up to the end of the line. Comments can begin at any column, and the may be inserted on the same line as Scheme code.

; Comment
;; Comment too
(define x 1)        ; Comment after expression
(let ((y 1))
  ;; Display something.
  (display y)
;;; Comment at left margin.
  (display (+ y 1)))

It is common to use a single semicolon for comments following expressions on a line, to use two semicolons for comments which are indented like code, and three semicolons for comments which start at column 0, even if they are inside an indented code block. This convention is used when indenting code in Emacs’ Scheme mode.