content/blog/haskell_lazy_evaluation.md

@@ -1,95 +0,0 @@
----
-title: "Clairvoyance for Good: Using Lazy Evaluation in Haskell"
-date: 2020-05-03T20:05:29-07:00
-tags: ["Haskell"]
-draft: true
----
-
-While tackling a project for work, I ran across a rather unpleasant problem.
-I don't think it's valuable to go into the specifics here (it's rather
-large and convoluted); however, the outcome of this experience led me to
-discover a very interesting technique for lazy functional languages,
-and I want to share what I learned.
-
-### Time Traveling
-Some time ago, I read [this post](https://kcsongor.github.io/time-travel-in-haskell-for-dummies/) by Csongor Kiss about time traveling in Haskell. It's
-really cool, and makes a lot of sense if you have wrapped your head around
-lazy evaluation. I'm going to present my take on it here, but please check out
-Csongor's original post if you are interested.
-
-Say that you have a list of integers, like `[3,2,6]`. Next, suppose that
-you want to find the maximum value in the list. You can implement such
-behavior quite simply with pattern matching:
-
-```Haskell
-myMax :: [Int] -> Int
-myMax [] = error "Being total sucks"
-myMax (x:xs) = max x $ myMax xs
-```
-
-You could even get fancy with a `fold`:
-
-```Haskell
-myMax :: [Int] -> Int
-myMax = foldr1 max
-```
-
-All is well, and this is rather elementary Haskell. But now let's look at
-something that Csongor calls the `repMax` problem:
-
-> Imagine you had a list, and you wanted to replace all the elements of the
-> list with the largest element, by only passing the list once.
-
-How can we possibly do this in one pass? First, we need to find the maximum
-element, and only then can we have something to replace the other numbers
-with! It turns out, though, that we can just expect to have the future
-value, and all will be well. Csongor provides the following example:
-
-```Haskell {linenos=table}
-repMax :: [Int] -> Int -> (Int, [Int])
-repMax [] rep = (rep, [])
-repMax [x] rep = (x, [rep])
-repMax (l : ls) rep = (m', rep : ls')
-  where (m, ls') = repMax ls rep
-        m' = max m l
-
-doRepMax :: [Int] -> [Int]
-doRepMax xs = xs'
-  where (largest, xs') = repMax xs largest
-```
-
-In the above snippet, `repMax` expects to receive the maximum value of
-its input list. At the same time, it also computes that maximum value,
-returning it and the newly created list. `doRepMax` is where the magic happens:
-the `where` clauses receives the maximum number from `repMax`, while at the
-same time using that maximum number to call `repMax`!
-
-This works because Haskell's evaluation model is, effectively,
-[lazy graph reduction](https://en.wikipedia.org/wiki/Graph_reduction). That is,
-you can think of Haskell as manipulating your code as
-{{< sidenote "right" "tree-note" "a syntax tree," >}}
-Why is it called graph reduction, you may be wondering, if the runtime is
-manipulating syntax trees? To save on work, if a program refers to the
-same value twice, Haskell has both of those references point to the
-exact same graph. This violates the tree's property of having only one path
-from the root to any node, and makes our program a graph. Graphs that
-refer to themselves also violate the properties of a tree.
-{{< /sidenote >}} performing
-substitutions and simplifications as necessary until it reaches a final answer.
-What the lazy part means is that parts of the syntax tree that are not yet
-needed to compute the final answer can exist, unsimplied, in the tree. This is
-what allows us to write the code above: the graph of `repMax xs largest`
-effectively refers to itself. While traversing the list, it places references
-to itself in place of each of the elements, and thanks to laziness, these
-references are not evaluated.
-
-Let's try a more complicated example. How about instead of creating a new list,
-we return a `Map` containing the number of times each number occured, but only
-when those numbers were a factor of the maximum numbers. Our expected output
-will be:
-
-```
->>> countMaxFactors [1,3,3,9]
-
-fromList [(1, 1), (3, 2), (9, 1)]
-```

themes/vanilla/assets/scss/sidenotes.scss

@@ -40,7 +40,7 @@ $sidenote-highlight-border-width: .2rem;
 }
 
 .sidenote-label {
-    border-bottom: .2rem dashed $primary-color;
+    border-bottom: .2rem solid $primary-color;
 }
 
 .sidenote-checkbox {

themes/vanilla/assets/scss/style.scss

@@ -14,10 +14,10 @@ h1, h2, h3, h4, h5, h6 {
   margin-top: .5rem;
   font-family: $font-heading;
   font-weight: normal;
-  text-align: center;
+  text-align: left;
 
   a {
-    border-bottom: none;
+    color: black;
 
     &:hover {
       color: $primary-color;
@@ -37,10 +37,6 @@ pre code {
     background-color: $code-color;
 }
 
-div.highlight table pre {
-    margin: 0;
-}
-
 .container {
   position: relative;
   margin: auto;
@@ -73,33 +69,28 @@ div.highlight table pre {
 }
 
 nav {
+  background-color: $primary-color;
   width: 100%;
-  margin: 0rem 0rem 1rem 0rem;
+  margin: 1rem 0rem 1rem 0rem;
-
-  .container {
-    display: flex;
-    justify-content: center;
-    flex-wrap: wrap;
 }
 
-  a {
+nav a {
-    padding: 0.25rem 0.75rem 0.25rem .75rem;
+  padding: .75em;
   text-decoration: none;
-    color: black;
+  color: white;
   display: inline-block;
-    border-bottom: none;
+
-    transition: color .25s;
+  transition: color .25s, background-color .25s;
-    white-space: nowrap;
 
   &:hover {
     color: $primary-color;
+    background-color: white;
   }
-  }
+
 }
 
 .post-subscript {
   color: #8f8f8f;
-  text-align: center;
 }
 
 .post-content {
@@ -131,9 +122,8 @@ h6 {
 }
 
 a {
-  color: black;
+  color: $primary-color-dark;
   text-decoration: none;
-  border-bottom: .2rem solid $primary-color;
 }
 
 img {
@@ -164,18 +154,6 @@ td {
     padding: 0.5rem;
 }
 
-hr.header-divider {
-    background-color: $primary-color;
-    height: 0.3rem;
-    border: none;
-    border-radius: 0.15rem;
-}
-
-ul.page-list a {
-  border-bottom: none;
-  font-weight: 700;
-}
-
 .katex-html {
     white-space: nowrap;
 }

themes/vanilla/layouts/_default/baseof.html

@@ -3,7 +3,6 @@
     {{- partial "head.html" . -}}
     <body>
         {{- partial "header.html" . -}}
-        <div class="container"><hr class="header-divider"></div>
         <main class="container">
         {{- block "main" . }}{{- end }}
         </main>

themes/vanilla/layouts/_default/list.html

@@ -1,7 +1,7 @@
 {{ define "main" }}
 <h2>{{ .Title }}</h2>
 
-<ul class="page-list">
+<ul>
     {{ range .Pages.ByDate.Reverse }}
     <li><a href="{{ .Permalink }}">{{ .Title }}</a></li>
     {{ end }}

themes/vanilla/layouts/blog/single.html

@@ -1,12 +1,12 @@
 {{ define "main" }}
 <h2>{{ .Title }}</h2>
 <div class="post-subscript">
-    <p>
+    <p>Posted on {{ .Date.Format "January 2, 2006" }}.</p>
+    <p>Tags:
         {{ range .Params.tags }}
         <a class="button" href="{{ $.Site.BaseURL }}/tags/{{ . | urlize }}">{{ . }}</a>
         {{ end }}
     </p>
-    <p>Posted on {{ .Date.Format "January 2, 2006" }}.</p>
 </div>
 
 <div class="post-content">

themes/vanilla/layouts/index.html

@@ -2,7 +2,7 @@
 {{ .Content }}
 
 Recent posts:
-<ul class="page-list">
+<ul>
 {{ range first 10 (where (where .Site.Pages.ByDate.Reverse "Section" "blog") ".Kind" "!=" "section") }}
 <li><a href="{{ .Permalink }}">{{ .Title }}</a></li>
 {{ end }}

themes/vanilla/layouts/partials/head.html

@@ -3,7 +3,7 @@
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <meta name="theme-color" content="#1dc868" />
 
-    <link href="https://fonts.googleapis.com/css2?family=Inconsolata&family=Raleway&family=Lora&display=swap" rel="stylesheet"> 
+    <link href="https://fonts.googleapis.com/css?family=Inconsolata|Lora|Raleway" rel="stylesheet">
     <link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/normalize/5.0.0/normalize.min.css">
     {{ $style := resources.Get "scss/style.scss" | resources.ToCSS | resources.Minify }}
     {{ $sidenotes := resources.Get "scss/sidenotes.scss" | resources.ToCSS | resources.Minify }}

themes/vanilla/layouts/tags/list.html

@@ -1,7 +1,7 @@
 {{ define "main" }}
 <h2>Tagged "{{ .Title }}"</h2>
 
-<ul class="page-list">
+<ul>
     {{ range .Pages.ByDate.Reverse }}
     <li><a href="{{ .Permalink }}">{{ .Title }}</a></li>
     {{ end }}

themes/vanilla/layouts/tags/terms.html

@@ -2,7 +2,7 @@
 <h2>{{ .Title }}</h2>
 Below is a list of all the tags ever used on this site.
 
-<ul class="page-list">
+<ul>
     {{ range sort .Pages "Title" }}
     <li><a href="{{ .Permalink }}">{{ .Title }}</a></li>
     {{ end }}