module Chapter3.IDesc.FreeMonad.Examples.FileSystem where
open import Data.Unit
open import Data.Nat hiding (_*_)
open import Data.Fin
open import Data.Vec hiding (_>>=_)
open import Data.Product
open import Data.String
open import Relation.Binary.PropositionalEquality
open import Chapter1.Logic
open import Chapter2.IDesc
open import Chapter2.IDesc.Tagged
open import Chapter2.IDesc.Fixpoint
open import Chapter3.IDesc.FreeMonad
open import Chapter3.IDesc.FreeMonad.IMonad
open import Chapter3.IDesc.FreeMonad.Monad
data State : Set where
Closed Open : State
infix 50 _⊢_
_⊢_ : {I : Set}(X : Set)(k : I) → Pow I
X ⊢ k = λ k' → k' ≡ k × X
ΣFS : tagDesc State
ΣFS = (0 , (λ _ → [])) ,
(λ { Closed → 1
; Open → 2 }) ,
(λ { Closed →
(`Σ String λ _ →
(`Π State λ s →
`Π ⊤ λ _ →
`var s) `× `1) ∷ []
; Open →
(`Π State λ s →
`Π (s ≡ Open × String) λ _ →
`var s) `× `1 ∷
(`Π State λ s →
`Π (s ≡ Closed × ⊤) λ _ →
`var s) `× `1 ∷ [] })
FS : (State → Set) → State → Set
FS = _*_ ΣFS
return : ∀{X} → X ⇒ FS X
return = `v {D = ΣFS}
openFile : (fname : String) → FS (λ _ → ⊤) Closed
openFile fname = ⟨ suc zero , fname , (λ s → return {X = λ _ → ⊤}) , tt ⟩
readFile : FS (λ s → s ≡ Open × String) Open
readFile = ⟨ suc zero , (λ s → return {X = String ⊢ Open}) , tt ⟩
closeFile : FS (λ s → s ≡ Closed × ⊤) Open
closeFile = ⟨ suc (suc zero) , (λ s → return {X = ⊤ ⊢ Closed}) , tt ⟩
example : FS (λ s → s ≡ Closed × String) Closed
example = openFile "test.txt" >>= λ {
{Closed} tt →
return (refl , "") ;
{Open} tt →
readFile >>= λ {
{Closed} (() , _) ;
{Open} (refl , str) →
closeFile >>= λ {
{Open} (() , _) ;
{Closed} (refl , tt) →
return (refl , str) }}}
where open RawIMonad (monad ΣFS) hiding (return)