[Agda] trouble with with

[Thorsten Altenkirch]

Hi guys,

inspired by Nisse's recent elaborations http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=96 
  I have been playing around with Agda (again) but in the moment I  
have a problem with with I don't really understand. Maybe somebody can  
advise me - it could be something obvious.

I define the finite sets as usual:

  data Fin : ℕ -> Set where
    fz : forall {n} -> Fin (succ n)
    fs : forall {n} -> Fin n -> Fin (succ n)

and implementations of the injections - sums are sums after all (I  
realize that it is arguable whether the first two arguments should be  
implicit):

  finl : forall {m n} -> Fin m -> Fin (m + n)
  finl fz     = fz
  finl (fs i) = fs (finl i)

  finr : forall {m n} -> Fin n -> Fin (m + n)
  finr {zero}   {n} i = i
  finr {succ m} {n} i = fs (finr {m} i)

and then I wanted to implement the view from section 3 of http://www.cs.nott.ac.uk/~txa/publ/ssgp06.pdf
but something goes wrong:

  data PlusView : forall {m n} -> Fin (m + n) -> Set where
    inl : forall {m n} -> (i : Fin m) -> PlusView {m} {n} (finl {m}  
{n} i)
    inr : forall {m n} -> (i : Fin n) -> PlusView {m} {n} (finr {m}  
{n} i)

  plusView : forall {m n} -> (i : Fin (m + n)) -> PlusView {m} {n} i
  plusView {zero}   {n} i      = inr {zero} {n} i
  plusView {succ m} {n} fz     = inl {succ m} {n} (fz {m})
  plusView {succ m} {n} (fs i) with plusView {m} {n} i
  plusView {succ m} {n} .(fs (finl {m} {n} j)) | (inl {.m} {.n} j) = ?
  plusView {succ m} {n} .(fs (finr {m} {n} j)) | (inr {.m} {.n} j) = ?

Agda isn't happy about my with-pattern:

/Users/txa/current/example.agda:30,3-32,71
With clause pattern .fs finl {m} {n} j is not an instance of its
parent pattern
when checking that the clause
plusView {(succ m)} {n} (fs i) with plusView {m} {n} i
plusView {(succ m')} {n'} .fs finl {m} {n} j | (inl {.m} {.n} j)
  = ?
plusView {(succ m')} {n'} .fs finr {m} {n} j | (inr {.m} {.n} j)
  = ?
has type {m : ℕ} {n : ℕ} (i : Fin (m + n)) -> PlusView i

I am using
Loading package Agda-2.1.2 ... linking ... done.
btw. Here is the file.
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Cheers,
Thorsten