X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=week9.mdwn;h=1992e207563a97504dfbbc1cbc154d0929d678d2;hp=c6dd9e83c05d965b5d7e5894f8d9932911a27d11;hb=8f043cd83b65c90928ab884d52be168b93d23a6c;hpb=bf8d964cc93f6b0b44a432bca8c94b1374c05e1f diff --git a/week9.mdwn b/week9.mdwn index c6dd9e83..1992e207 100644 --- a/week9.mdwn +++ b/week9.mdwn @@ -429,7 +429,7 @@ Here's how to implement these. We'll suppose that our assignment function is lis (* evaluate expr2 using original assignment function and new store *) in eval expr2 g s'' -Note: Chris uses this kind of machinery on the third page of the Nov 22 handout. Except he implements `Let` the way we here implement `Change`. And he adds an implementation of `Alias` (see below). Some minor differences: on his handout (and following Groenendijk, Stockhof and Veltman), he uses `r` and `g` where we use `g` and `s` respectively. Also, he implements his `r` with a function from `char` to `int`, instead of a `(char * int) list`, as we do here. It should be obvious how to translate between these. His implementation requires that variables always already have an associated peg. So that when we call `Let(c, expr1, expr2)` for the first time with `c`, there's a peg whose value is to be updated. That's easier to ensure when you implement the assignment as a function than as a `(char * int) list`. +Note: Chris uses this kind of machinery on the third page of the Nov 22 handout. Except he implements `Let` the way we here implement `Change`. And he adds an implementation of `Alias` (see below). Some minor differences: on his handout (and following Groenendijk, Stokhof and Veltman), he uses `r` and `g` where we use `g` and `s` respectively. Also, he implements his `r` with a function from `char` to `int`, instead of a `(char * int) list`, as we do here. It should be obvious how to translate between these. His implementation requires that variables always already have an associated peg. So that when we call `Let(c, expr1, expr2)` for the first time with `c`, there's a peg whose value is to be updated. That's easier to ensure when you implement the assignment as a function than as a `(char * int) list`. ##How to implement mutation with a State monad## @@ -503,6 +503,8 @@ To get the whole process started, the complex computation so defined will need t in computation initial_store;; +* See also our [[State Monad Tutorial]]. + ##Aliasing or Passing by reference## @@ -751,7 +753,7 @@ Programming languages tend to provide a bunch of mutation-related capabilities a In point 7 of the Rosetta Stone discussion, the contrast between call-by-name and call-by-value evaluation order appears (though we don't yet call it that). We'll be discussing that more in coming weeks. In the [[damn]] example, continuations and other kinds of side-effects (namely, printing) make an appearance. These too will be center-stage in coming weeks. -* Now would also be a good time to read [[Advanced Topics/Calculator Improvements]]. This reviews the different systems discussed above, as well as other capabilities we can add to the calculators introduced in [week7](/reader_monad_for_variable_binding). We will be building off of that in coming weeks. +* Now would also be a good time to read [Calculator Improvements](/week10). This reviews the different systems discussed above, as well as other capabilities we can add to the calculators introduced in [week7](/reader_monad_for_variable_binding). We will be building off of that in coming weeks. ##Offsite Reading##