[Haskell-beginners] Reducing local variable duplication

29 Aug 2011


      I have a series of unit tests like this,
...
test_volume1 :: Assertion
test_volume1 =
  assertEqual "volume is correct" True (vol ~= (-1/3))
  where
    p0 = (0, -0.5, 0)
    p1 = (0, 0.5, 0)
    p2 = (2, 0, 0)
    p3 = (1, 0, 1)
    ...
test_volume2 :: Assertion
test_volume2 =
  assertEqual "volume is correct" True (vol ~= (1/3))
  where
    p0 = (0, -0.5, 0)
    p1 = (2, 0, 0)
    p2 = (0, 0.5, 0)
    p3 = (1, 0, 1)
    ...
I would like to de-duplicate some of the values in the 'where' clause.
Furthermore, I don't want to declare e.g. p0 and p3 at the top level,
since later tests may need different values of p0,p3. What I would
really like is something like the following. Is it possible?
...
let p0 = (0, -0.5, 0)
    p3 = (1, 0, 1)
in
  test_volume1 :: Assertion
  test_volume1 =
    assertEqual "volume is correct" True (vol ~= (-1/3))
    where
      p1 = (0, 0.5, 0)
      p2 = (2, 0, 0)
      ...
test_volume2 :: Assertion
  test_volume2 =
    assertEqual "volume is correct" True (vol ~= (1/3))
    where
      p1 = (2, 0, 0)
      p2 = (0, 0.5, 0)
      ...

[Haskell-beginners] Reducing local variable duplication

Michael Orlitzky