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Danila Fedorin 2020-11-02 01:08:41 -08:00
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content/blog/typesafe_imperative_lang.md
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---
title: "A Typesafe Representation of an Imperative Language"
date: 2020-10-30T17:19:59-07:00
date: 2020-11-02T01:07:21-08:00
tags: ["Idris"]
draft: true
---
A recent homework assignment for my university's programming languages
@ -85,7 +84,7 @@ can evaluate to either a boolean or an integer value (because a register
can contain either of those types of values). Perhaps we can specify
the type that an expression evaluates to in the expression's own type:
`Expr IntTy` would evaluate to integers, and `Expr BoolTy` would evaluate
to booleans. Then, we could constructors as follows:
to booleans. Then, we could have constructors as follows:
```Idris
Lit : Int -> Expr IntTy
@ -360,7 +359,7 @@ pattern matching:
The `getReg` function will take out the value of the corresponding
register, returning `Int` or `Bool` depending on the `TypeState`.
What's important is that if the `TypeState` is known, then so
is the type of `getReg`: no `Either` is involved her, and we
is the type of `getReg`: no `Either` is involved here, and we
can directly use the integer or boolean stored in the
register. This is exactly what we do:
@ -453,7 +452,7 @@ We then have:
MkState (0, 9, 63) : State (IntTy, IntTy, IntTy)
```
Which seems correct! The program multiplies seven by nine,
This seems correct! The program multiplies seven by nine,
and stops when register `A` reaches zero. Our test program
runs, too:
@ -473,7 +472,5 @@ aren't possible: our programs are guaranteed to be
{{< sidenote "right" "termination-note" "type correct." >}}
Our programs <em>aren't</em> guaranteed to terminate:
we're lucky that Idris' totality checker is turned off by default.
{{< /sidenote >}}
This was a fun exercise, and I hope you enjoyed reading along!
{{< /sidenote >}} This was a fun exercise, and I hope you enjoyed reading along!
I hope to see you in my future posts.