yes you can, it's actually better to encapsulate all "lambdas" and intermediate values inside one function, provided you never use them anywhere else.
i advise using "where" as such:

md n = dist (Point (fx n) (fy n)) (Point (gx n) (gy n))
  where fx n = 4.0 + 0.5 * n
        fy n = 4.0 - 0.5 * n
        gx n = n * 1.0
        gy n = n * (-1.0)
-- then you can call "foo = md 2"

it's more idiomatic to use where, i believe. however you can also choose to define the helpers before the expression defining the function, using "let ... in" like that:

md n = let fx n = 4.0 + 0.5 * n
           fy n = 4.0 - 0.5 * n
           gx n = n * 1.0
           gy n = n * (-1.0)
       in dist (Point (fx n) (fy n)) (Point (gx n) (gy n))

be careful about the alignment. both ways are (in this example) strictly equivalent, it all depends on circumstances and taste.

mind you if you don't want a function to be reused, merely one single value foo = md 2, you can always just write directly:
foo = dist (Point (fx 2) (fy 2)) (Point (gx 2) (gy 2))
  where fx n = 4.0 + 0.5 * n
        fy n = 4.0 - 0.5 * n
        gx n = n * 1.0
        gy n = n * (-1.0)

2017-06-26 11:38 GMT+02:00 PATRICK BROWNE <patrick.browne@dit.ie>:
The code below provides a distance function that works for points and moving point.
I am happy with the result, but I have a problem with the lambda expressions.
Instead of supplying an argument to each 'mpXX', is it possible to have a single lambda argument on the entire final 'md' function? (e.g. 'md 2')
Thanks in advance,
Pat

data Point a = Point { abscissa :: a, ordinate :: a } deriving Show
dist a b = sqrt (((abscissa a) - (abscissa b))^2 + ((ordinate a) - (ordinate b))^2)

-- Sttic points
p1, p2 :: Point Float
p1 = Point 0.0 0.0
p2 = Point 4.0 4.0
d = dist p1 p2


-- Moving points
mp1, mp2 :: Point Float
mp1x = (\t -> 4.0 + 0.5 * t)
mp1y = (\t -> 4.0 - 0.5 * t)
mp1 = Point (mp1x 2) (mp1y  2)
mp2x  = (\t -> 0.0 + 1.0 * t)
mp2y  = (\t -> 0.0 - 1.0 * t)
mp2 = Point (mp2x 2) (mp2y 2)
md = dist mp1 mp2

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