lazyFibs animation

Author: tgdwyer

Gemfile.lock

@@ -11,7 +11,7 @@ GEM
     eventmachine (1.2.7)
     ffi (1.17.0-arm64-darwin)
     ffi (1.17.0-x64-mingw-ucrt)
-    ffi (1.17.0-x86_64-linux-gnu)
+    ffi (1.17.0-x86_64-linux)
     forwardable-extended (2.6.0)
     http_parser.rb (0.8.0)
     i18n (1.14.5)
@@ -64,7 +64,7 @@ GEM
       racc (~> 1.4)
     nokogiri (1.18.9-x64-mingw-ucrt)
       racc (~> 1.4)
-    nokogiri (1.18.9-x86_64-linux-gnu)
+    nokogiri (1.18.9-x86_64-linux)
       racc (~> 1.4)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
@@ -86,6 +86,7 @@ GEM
     tzinfo-data (1.2024.1)
       tzinfo (>= 1.0.0)
     unicode-display_width (2.5.0)
+    wdm (0.1.1)
     webrick (1.8.2)
 
 PLATFORMS
@@ -102,6 +103,7 @@ DEPENDENCIES
   minima
   nokogiri
   tzinfo-data
+  wdm (~> 0.1.0)
   webrick
 
 BUNDLED WITH

_chapters/haskell1.md

@@ -405,6 +405,21 @@ fibs n = case n of
 
 </div>
 
+## A lazy infinite sequence
+
+Let's briefly revisit fibonacci numbers and demonstrate a very idiomatic haskell construction for defining a lazy sequence.  In the following definition for `lazyFibs`, `zipWith` is a function which uses the specified function (in this case `(+)`) to pair the heads of two given lists.  In this case, we are zipping over recursive references to `lazyFibs` and `tail lazyFibs`.
+
+```haskell
+lazyFibs = 1 : 1 : zipWith (+) lazyFibs (tail lazyFibs)
+```
+We can then create as much of the list as we need:
+```haskell
+take 10 lazyFibs
+[1,1,2,3,5,8,13,21,34,55]
+```
+This is only possible because Haskell's lazy evaluation only forces evaluation of the heads of the lists as necessary, e.g. to output the result of `take 10`.
+![Deck Observable Visualised](/assets/images/chapterImages/haskell1/zip.gif)
+
 ## Glossary
 
 *GHCi REPL*: The interactive Read-Eval-Print Loop for GHC, the Glasgow Haskell Compiler, allowing users to test Haskell programs and expressions interactively.