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@@ -103,6 +103,17 @@ needed to compute the final answer can exist, unsimplified, in the tree.
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Why don't we draw a few graphs to get familiar with the idea?
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### Visualizing Graphs and Their Reduction
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__A word of caution__: the steps presented below may significantly differ
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from the actual graph reduction algorithms used by modern compilers.
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In particular, this section draws a lot of ideas from Simon Peyton Jones' book,
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[_Implementing functional languages: a tutorial_](https://www.microsoft.com/en-us/research/publication/implementing-functional-languages-a-tutorial/).
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However, modern functional compilers (i.e. GHC) use a much more
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complicated abstract machine for evaluating graph-based code,
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based on -- from what I know -- the [spineless tagless G-machine](https://www.microsoft.com/en-us/research/wp-content/uploads/1992/04/spineless-tagless-gmachine.pdf).
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In short, this section, in order to build intuition, walks through how a functional program
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evaluated using graph reduction _may_ behave; the actual details
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depend on the compiler.
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Let's start with something that doesn't have anything fancy. We can
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take a look at the graph of the expression:
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@@ -361,7 +361,7 @@ I think this is a good approach. Should we want to add more types to our languag
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lists, and so on, we will be able to extend our `decEq` approach to construct more complex equality
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proofs, and keep the `typecheck` method the same. Had we not used this approach,
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and instead decided to pattern match on types inside of `typecheck`, we would've quickly
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found that this only works for types with finitely many values. When we add polymorphic tuples
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found that this only works for languages with finitely many types. When we add polymorphic tuples
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and lists, we start being able to construct an arbitrary number of types: `[a]`. `[[a]]`, and
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so on. Then, we cease to be able to enumerate all possible pairs of types, and require a recursive
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solution. I think that this leads us back to `decEq`.
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@@ -1,8 +1,7 @@
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---
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title: Meaningfully Typechecking a Language in Idris, With Tuples
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date: 2020-08-11T19:57:26-07:00
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date: 2020-08-12T15:48:04-07:00
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tags: ["Idris"]
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draft: true
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---
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Some time ago, I wrote a post titled
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@@ -28,6 +28,7 @@ pre code {
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border: $code-border;
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display: block;
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overflow: auto;
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margin-bottom: 1rem;
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td {
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padding: 0;
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