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Apr 21st, 2019
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__Sign Up__- diff :: [(a,b)] -> [c]
- diff [] = []
- diff ((a,b):xs) = (a-b):(diff xs)
- GHCI ERROR MESSAGES:
- addprime.hs:3:19: error:
- • Couldn't match type ‘a’ with ‘c’
- ‘a’ is a rigid type variable bound by
- the type signature for:
- diff :: forall a b c. [(a, b)] -> [c]
- at addprime.hs:1:1-22
- ‘c’ is a rigid type variable bound by
- the type signature for:
- diff :: forall a b c. [(a, b)] -> [c]
- at addprime.hs:1:1-22
- Expected type: [c]
- Actual type: [a]
- • In the expression: (a - b) : (diff xs)
- In an equation for ‘diff’: diff ((a, b) : xs) = (a - b) : (diff xs)
- • Relevant bindings include
- xs :: [(a, b)] (bound at addprime.hs:3:13)
- a :: a (bound at addprime.hs:3:8)
- diff :: [(a, b)] -> [c] (bound at addprime.hs:2:1)
- |
- 3 | diff ((a,b):xs) = (a-b):(diff xs)
- | ^^^^^^^^^^^^^^^
- addprime.hs:3:22: error:
- • Couldn't match expected type ‘a’ with actual type ‘b’
- ‘b’ is a rigid type variable bound by
- the type signature for:
- diff :: forall a b c. [(a, b)] -> [c]
- at addprime.hs:1:1-22
- ‘a’ is a rigid type variable bound by
- the type signature for:
- diff :: forall a b c. [(a, b)] -> [c]
- at addprime.hs:1:1-22
- • In the second argument of ‘(-)’, namely ‘b’
- In the first argument of ‘(:)’, namely ‘(a - b)’
- In the expression: (a - b) : (diff xs)
- • Relevant bindings include
- xs :: [(a, b)] (bound at addprime.hs:3:13)
- b :: b (bound at addprime.hs:3:10)
- a :: a (bound at addprime.hs:3:8)
- diff :: [(a, b)] -> [c] (bound at addprime.hs:2:1)
- |
- 3 | diff ((a,b):xs) = (a-b):(diff xs)
- | ^
- Failed, no modules loaded.

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