fixpoint "--rewrite"

data Blob 0 = [ 
  | VBlob { vgoo : Int } 
  ]

data Vec 1 = [
  | VCons { vhead : @(0) } 
]

constant len : (func(1, [(Vec @(0)); int]))
constant hen : (func(1, [Blob; int]))
constant tt  : (Vec bool)
constant bob : (Blob)
constant foo : (func(0, [Blob; Blob]))

match hen VBlob z = 10 

match len VCons x = (hen (foo (VBlob 12)))

bind 0 thing : {v: int | true} 

constraint:
  env [0]
  lhs {v : int | len (VCons 1) = 10 }
  rhs {v : int | len (VCons 1) = 10 }
  id 1 tag []

expand [1 : True]