after a () succeed to run
On Tuesday, July 19, 2016 at 11:28:03 AM UTC+8, meInvent bbird wrote:
it return Maybe [Double]
and fromJust can remove Maybe
but error in this case
*Main Data.Map Map Data.Maybe> :t fromJust
fromJust :: Maybe a -> a
*Main Data.Map Map Data.Maybe> :type sequence [Map.lookup (input2!!i,input1!!i) $ op1 | i <- [0..3]]
sequence [Map.lookup (input2!!i,input1!!i) $ op1 | i <- [0..3]]
:: Maybe [Double]
*Main Data.Map Map Data.Maybe> fromJust sequence [Map.lookup (input2!!i,input1!!i) $ op1 | i <- [0..3]]
<interactive>:32:10:
Couldn't match expected type `Maybe ([Maybe Double] -> t0)'
with actual type `[m0 a0] -> m0 [a0]'
In the first argument of `fromJust', namely `sequence'
In the expression:
fromJust
sequence
[Map.lookup (input2 !! i, input1 !! i) $ op1 | i <- [0 .. 3]]
In an equation for `it':
it
= fromJust
sequence
[Map.lookup (input2 !! i, input1 !! i) $ op1 | i <- [0 .. 3]] *Main Data.Map Map Data.Maybe>
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