From: jim Date: Wed, 4 Feb 2015 16:15:30 +0000 (-0500) Subject: fix typo, thanks Kyle X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=8d0fcac289637208d8f22cbfba091e47ecb1a39f fix typo, thanks Kyle --- diff --git a/topics/week1_advanced_notes.mdwn b/topics/week1_advanced_notes.mdwn index c5e589f2..8b6289a6 100644 --- a/topics/week1_advanced_notes.mdwn +++ b/topics/week1_advanced_notes.mdwn @@ -102,7 +102,7 @@ If we get to the `y & ys` line in the pattern list, and the pattern-match succee Sometimes it's useful to bind variables against overlapping parts of a structure. For instance, suppose I'm writing a pattern that is to be matched against multivalues like `([10, 20], 'true)`. And suppose I want to end up with `ys` bound to `[10, 20]`, `x` bound to `10`, and `xs` bound to `[20]`. Using the techniques introduced so far, I have two options. First, I could bind `ys` against `[10, 20]`, and then initiate a second pattern-match to break that up into `10` and `[20]`. Like this: case ([10, 20], 'true) of - [ys, _] then case ys of + (ys, _) then case ys of x & xs then ...; ... end; @@ -112,7 +112,7 @@ Sometimes it's useful to bind variables against overlapping parts of a structure Alternatively, I could directly bind `x` against `10` and `xs` against `[20]`. But then I would have to re-cons them together again to get `ys`. Like this: case ([10, 20], 'true) of - [x & xs, _] then let + (x & xs, _) then let ys match x & xs in ...; ... @@ -121,7 +121,7 @@ Alternatively, I could directly bind `x` against `10` and `xs` against `[20]`. B Both of these strategies work. But they are a bit inefficient. I said you didn't really need to worry about efficiency in this seminar. But these are also a bit cumbersome to write. There's a special syntax that enables us to bind all three of `ys`, `x`, and `xs` in the desired way, despite the fact that they will be matching against overlapping, rather than discrete, parts of the value `[10, 20]`. The special syntax looks like this: case ([10, 20], 'true) of - [(x & xs) as ys, _] then ... + ((x & xs) as ys, _) then ... ... end