From: Jim Date: Sun, 1 Feb 2015 10:34:55 +0000 (-0500) Subject: update week1 notes X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=b8c16eb9c7dd7208868b4ef1a7175fe86698287f update week1 notes --- diff --git a/week1.mdwn b/week1.mdwn index b724a1ba..983c18c0 100644 --- a/week1.mdwn +++ b/week1.mdwn @@ -594,9 +594,9 @@ the variable `x` has not been *overwritten* (mutated). Rather, we have *two* var evaluates to? Well, consider the right-hand side of the second binding: -   let -   x match x + 1 -   in (x, 2*x) + let + x match x + 1 + in (x, 2*x) This expression evaluates to `(1, 2)`, because it uses the outer binding of `x` to `0` for the right-hand side of its own binding `x match x + 1`. That gives us a new binding of `x` to `1`, which is in place when we evaluate `(x, 2*x)`. That's why the whole thing evaluates to `(1, 2)`. So now returning to the outer expression, `y` gets bound to `1` and `z` to `2`. But now what is `x` bound to in the final line,`([y, z], x)`? The binding of `x` to `1` was in place only until we got to `(x, 2*x)`. After that its scope expired, and the original binding of `x` to `0` reappears. So the final line evaluates to `([1, 2], 0)`.