Type-level SEO with Idris

Jan Schulte

What is SEO?

How can we improve?

Pay tons of $$$ on adverts
Optimise web site for search engines

https://static.googleusercontent.com/media/www.google.com/de//webmasters/docs/search-engine-optimization-starter-guide.pdf

Rule 1 - Simple-to-understand URLs

- avoid using odd capitalization of URLs

- /This/IS/not/s3o-{frI3ndLy}

Rule 2 - Simple directory structure

- Avoid having deep nesting of subdirectories like ".../dir1/dir2/dir3/dir4/dir5/dir6/page.html"

Rule 3 - Complete directory structure

- Allow for the possibility of a part of the URL being removed

Motivation

Avoiding SEO problems is hard
Enforce our rules as early as possible!

⇒ Proof of concept using dependent types in Idris

Site aka URL structure

Routing DSL: Spring


@GetMapping("/sports/basketball")
public ModelMap basketballHandler() {
    ... 
}

Routing DSL: Play


GET  /sports/basketball  SportsController.basketballHandler

Goal:

Create SEO-conform Routing DSL

Idris routing DSL

Routes (
  GET  Root homepageHandler &
  GET (Root / Literal "sports") sportsHandler &
  GET (Root / Literal "sports" / Literal "basketball") basketballHandler 
)

Compiles

Does not compile

Follows SEO rules?

Breaks SEO rules?

Procedure

Route element
Route
Many routes

Routes (
  GET  Root homepageHandler &
  GET (Root / Literal "sports") sportsHandler &
  GET (Root / Literal "sports" / Literal "basketball") basketballHandler 
)

Idris

data Option : (t:Type) -> Type where
  Some : (value:t) -> Option t
  None : Option t

add : Int -> Int -> Int
add x y = x + y

*intro> Some 5
Some 5 : Option Integer

data List : (elem : Type) -> Type where

data Vect : (len : Nat) -> (elem : Type) -> Type where

Idris> [1,2,3]
[1, 2, 3] : List Int

Idris> the (Vect _ Int) [1,2,3]
[1, 2, 3] : Vect 3 Int

StringOrNat : Nat -> Type
StringOrNat Z = String
StringOrNat (S n) = Nat

divide : (x:Nat) -> (y:Nat) -> StringOrNat y
divide x Z = "Divisor was 0"
divide x y @ (S n) = div x y

Idris> divide 10 2
5 : Nat

Idris> divide 10 0
"Divisor was 0" : String

Rule 1 - Simple-to-understand URLs

- avoid using odd capitalization of URLs

- /This/IS/not/s3o-{frI3ndLy}

Rule 1

Root / Literal "seo-friendly"

Root / Literal "{no_~.-$Eo-fRiEndLy}^"

Should compile

Should not

compile

Rule 2 - Simple directory structure

- Avoid having deep nesting of subdirectories like ".../dir1/dir2/dir3/dir4/dir5/dir6/page.html"

Rule 2

Root / Literal "category" / Literal "sports" / Literal "football"

Root / Literal "category" / Literal "sports" / Literal "ball" / Literal "round" / Literal "foot"

Should compile

Should not compile

Rule 3 - Complete directory structure

- Allow for the possibility of a part of the URL being removed

Rule 3

GET Root homepageHandler
GET Root / Literal "sports" sportsHandler
GET Root / Literal "sports" / Literal "football" footballHandler

Should compile

Should not compile

GET Root homepageHandler
GET Root / Literal "sports" / Literal "football" footballHandler

Summary

Routing DSL
Compile-time SEO checks
No macro's - plain Idris
Automatic proof finding
Many more SEO rules

compile-time correspondance

curry data dependent function hole howard idris

implicit isomorphism lambda logic monad php proof rankingroutes search seo static types

Thank you!

{slides,github}.com/janschultecom/typelevel-seo

@janschultecom

Hic sunt dracones

About me

Independent Software Consultant
Scala for work
Idris for fun

Rule 4 - Use relevant words in URLs

- URLs with words that are relevant to your site's content and structure are friendlier for visitors navigating your site.

Rule 4

Root / Literal "has-football-keyword"

Root / Literal "eyjafjallajokull"

Should compile

Should not

compile

Root / Literal "has-no-keyword"

Should not

compile

Root / Literal "basketball"

Should compile

Typelevel SEO with Idris

By Jan Schulte