Enhance comments

lib/comprewrite.stk

@@ -180,7 +180,7 @@
 (define (no-srfi-5-let? form)
   ;; form = (LET A B ...)
   ;; (CADR form) = A
-  ;; (CAADR form (CAR A)
+  ;; (CAADR form) = (CAR A)
   (or (not (pair? (cadr form))) ; named LET, not SRFI-5 LET
       (list? (caadr form))))    ; CAR of bindings is list, not SRFI-5 LET
 
@@ -196,7 +196,7 @@
         (else #f)))
 
 ;; (internal-shadow? bindings) will check if the bindings would
-;; LET their own variable definition if truned into a LET*.
+;; LET their own variable definition if turned into a LET*.
 ;; For example:
 ;;
 ;; (let ((a 10)
@@ -253,7 +253,12 @@
 ;; See that the bodies of the LETs are appended, reflecting the order
 ;; in which the expressions would be executed.
 ;;
-;; Shadowing LETs are not optimized, as this can lead to wrong results.
+;; These are not optimized, as this can lead to wrong results:
+;; - a LET that would shadow a variable in an outer let
+;; - a LET that uses a symbol that it also defines:
+;;   (LET ((a ...) (b ... a ...)) ...)
+;; - SRFI-5 LETs
+;; - named LETs
 (define (join-lets expression)
   ;; (let1 bindings1 (let2 bindings2 . body2) . body1)
   ;;