week9 tweak

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

diff --git a/week9.mdwn b/week9.mdwn
index f854d27..721dde5 100644 (file)
--- a/week9.mdwn
+++ b/week9.mdwn
@@ -696,7 +696,7 @@ Programming languages tend to provide a bunch of mutation-related capabilities a
                in let (adder', setter') = factory 1
                in ...
 
                in let (adder', setter') = factory 1
                in ...
 

-       Of course, in most languages you wouldn't be able to evaluate a comparison like `getter = getter'`, because in general the question whether two functions always return the same values for the same arguments is not decidable. So typically languages don't even try to answer that question. However, it would still be true that `getter` and `getter'` (and `adder` and `adder'`) were extensionally equivalent.
+       Of course, in most languages you wouldn't be able to evaluate a comparison like `getter = getter'`, because in general the question whether two functions always return the same values for the same arguments is not decidable. So typically languages don't even try to answer that question. However, it would still be true that `getter` and `getter'` (and `adder` and `adder'`) were extensionally equivalent; you just wouldn't be able to establish so.

 
        However, they're not numerically identical, because by calling `setter 2` (but not calling `setter' 2`) we can mutate the function value `getter` (and `adder`) so that it's *no longer* qualitatively indiscernible from `getter'` (or `adder'`).
 
 
        However, they're not numerically identical, because by calling `setter 2` (but not calling `setter' 2`) we can mutate the function value `getter` (and `adder`) so that it's *no longer* qualitatively indiscernible from `getter'` (or `adder'`).