Expr.dhall

let Expr
    : Type → Type
    = λ(A : Type) →
        ∀(Expr : Type → Type) →
        ∀(If : { cond : Text, thenE : Expr A, elseE : Expr A } → Expr A) →
        ∀(Ref : Text → Expr A) →
        ∀(Lit : A → Expr A) →
          Expr A

let example
    : Expr Natural
    = λ(Expr : Type → Type) →
      λ ( If
        : { cond : Text, thenE : Expr Natural, elseE : Expr Natural } →
            Expr Natural
        ) →
      λ(Ref : Text → Expr Natural) →
      λ(Lit : Natural → Expr Natural) →
        If { cond = "asdf", thenE = Ref "bsdf", elseE = Lit 42 }

let atoms =
      λ(A : Type) →
      λ(expr : Expr A) →
         expr
              (λ(ignored : Type) → List Text)
              ( λ(If : { cond : Text, thenE : List Text, elseE : List Text }) →
                  [ If.cond ] # If.thenE # If.elseE
              )
              (λ(Ref : Text) → [ Ref ])
              (λ(Lit : A) → [] : List Text)

in  atoms Natural example