Re: [Haskell-beginners] Improve my lambda expressions
Thanks for all your help.
I was unaware that there was a relation between let/where and lambdas.
Here is my effort to use a single lamda
md3 n = (\n -> (dist (Point (4.0 + 0.5 * n) (4.0 - 0.5 * n)) (Point (n *
1.0) ( n * (-1.0))))) n
I imagine that this function could be written without lambdas, let, or
where.
Is it generally true the all/most functions could be written without
lambdas, let, or where?
Thanks,
Pat
On 26 June 2017 at 12:04, Frerich Raabe
On 2017-06-26 11:38, PATRICK BROWNE wrote:
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.
[..]
-- 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
Maybe you could reduce the number of lambda expressions by extracting common logic. It seems to me that 'mp1' and 'mp2' are moved versions of the same point (2,2) except that they apply different functions to the coordinates. These functions follow a pattern (a factor is applied to the component and then an 'offset' is added).
For instance, it might be worthwhile to define
movePoint :: Float -> Float -> Point -> Point movePoint offset factor (Point x y) = Point (offset + factor * x) (offset - factor * y)
...such that you could then define
md = let p = Point 2 2 in dist (movePoint 4 0.5 p) (movePoint 0 1 p)
-- Frerich Raabe - raabe@froglogic.com www.froglogic.com - Multi-Platform GUI Testing
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On 2017-06-27 18:35, PATRICK BROWNE wrote:
Thanks for all your help. I was unaware that there was a relation between let/where and lambdas. Here is my effort to use a single lamda md3 n = (\n -> (dist (Point (4.0 + 0.5 * n) (4.0 - 0.5 * n)) (Point (n * 1.0) ( n * (-1.0))))) n
I imagine that this function could be written without lambdas, let, or where.
Indeed, it could. Note that your definition has the form md3 n = (\n -> (dist )) n I.e. the expression 'md3 n' is equivalent to the expression '(\n -> (dist ..)) n', which means 'apply the lambda expression to n'. You don't need the lambda expression if you apply it to a given argument directly though, i.e. the above definition is equivalent to md3 n = dist ..
Is it generally true the all/most functions could be written without lambdas, let, or where?
I believe it is true since you could define any function as a global definition (i.e. not a nested scope as in let..in or where). -- Frerich Raabe - raabe@froglogic.com www.froglogic.com - Multi-Platform GUI Testing
participants (2)
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Frerich Raabe -
PATRICK BROWNE