week1: fix markup processing?

Signed-off-by: Jim Pryor <profjim@jimpryor.net>

diff --git a/test2.mdwn b/test2.mdwn
index afe1b69..dcc8a1a 100644 (file)
--- a/test2.mdwn
+++ b/test2.mdwn
@@ -601,3 +601,80 @@ Here's how it looks to say the same thing in various of these languages.
 
        It's easy to be lulled into thinking this is a kind of imperative construction. *But it's not!* It's really just a shorthand for the compound "let"-expressions we've already been looking at, taking the maximum syntactically permissible scope. (Compare the "dot" convention in the lambda calculus, discussed above.)
 
 
        It's easy to be lulled into thinking this is a kind of imperative construction. *But it's not!* It's really just a shorthand for the compound "let"-expressions we've already been looking at, taking the maximum syntactically permissible scope. (Compare the "dot" convention in the lambda calculus, discussed above.)
 

+
+9.     Some shorthand
+
+       OCaml permits you to abbreviate:
+
+               let bar = fun x -> B in
+                       M
+
+       as:
+
+               let bar x = B in
+                       M
+
+       It also permits you to abbreviate:
+
+               let bar = fun x -> B;;
+
+       as:
+
+               let bar x = B;;
+
+       Similarly, Scheme permits you to abbreviate:
+
+               (define bar (lambda (x) B))
+
+       as:
+
+               (define (bar x) B)
+
+       and this is the form you'll most often see Scheme definitions written in.
+
+       However, conceptually you should think backwards through the abbreviations and equivalences we've just presented.
+
+               (define (bar x) B)
+
+       just means:
+
+               (define bar (lambda (x) B))
+
+       which just means:
+
+               (let* [(bar (lambda (x) B))] ... rest of the file or interactive session ...)
+
+       which just means:
+
+               (lambda (bar) ... rest of the file or interactive session ...) (lambda (x) B)
+
+       or in other words, interpret the rest of the file or interactive session with `bar` assigned the function `(lambda (x) B)`.
+
+
+10.    Shadowing
+
+       You can override a binding with a more inner binding to the same variable. For instance the following expression in OCaml:
+
+               let x = 3 in
+                       let x = 2 in
+                               x
+
+       will evaluate to 2, not to 3. It's easy to be lulled into thinking this is the same as what happens when we say in C:
+
+               int x = 3;
+               x = 2;
+       
+       <em>but it's not the same!</em> In the latter case we have mutation, in the former case we don't. You will learn to recognize the difference as we proceed.
+
+       The OCaml expression just means:
+
+               (fun x -> ((fun x -> x) 2) 3)
+
+       and there's no more mutation going on there than there is in:
+
+       <pre>
+       <code>&forall;x. (F x or &forall;x (not (F x)))</code>
+       </pre>
+
+       When a previously-bound variable is rebound in the way we see here, that's called **shadowing**: the outer binding is shadowed during the scope of the inner binding.
+