Idris2/tests/ttimp/qtt002/QTT.yaff

data Nat : Type where
     Z : Nat
     S : Nat -> Nat

plus : Nat -> Nat -> Nat
plus Z $y = y
plus (S $k) $y = S (plus k y)

data Vect : Nat -> Type -> Type where
     Nil : Vect Z $a
     Cons : $a -> (1 xs : Vect $k $a) -> Vect (S $k) $a

append : (1 xs : Vect $n $a) -> Vect $m $a -> Vect (plus $n $m) $a
append (Cons $x zs@(Cons $y $ws)) $ys = ?foo -- zs usable, y+ws not

cappend : (1 xs : Vect $n $a) -> Vect $m $a -> Vect (plus $n $m) $a
cappend $xs $ys
    = case xs of
           Nil => ys
           Cons $x $zs => ?bar -- zs usable, xs not

cappend2 : (1 xs : Vect $n $a) -> Vect $m $a -> Vect (plus $n $m) $a
cappend2 $xs $ys
    = case xs of
           Nil => ys
           Cons $x $zs => let ts = zs in ?baz -- ts usable, xs+zs not