-- works ----------------------

calcedLayer = foldl' k [] rl
k c n = c `seq` c ++ [updateN n]
updateN n = updateNeuron n (v_inputSum n) (v_state n) (weights n)
v_inputSum n = calcNeuron ll (weights n)
v_state n = sigmoidFunction (v_inputSum n)

-- don't work ----------------------
{--
src/Backpropagation.hs:149:22:
    Couldn't match expected type `([Neuron], [Neuron])'
           against inferred type `[Neuron]'
    In the first argument of `foldl'', namely `updateNeuronList'
    In the expression: foldl' updateNeuronList ([], ll) rl
    In the definition of `calcedLayer':
        calcedLayer = foldl' updateNeuronList ([], ll) rl
--}
calcLayer :: [Neuron] -> [Neuron] -> [Neuron]
calcLayer ll rl = calcedLayer where
	calcedLayer = foldl' updateNeuronList ([], ll) rl

-- update layer of neurons
-- avoiding unneeded laziness
updateNeuronList :: ([Neuron], [Neuron]) -> Neuron -> [Neuron]
updateNeuronList (x, ll) n = x `seq` ll `seq` (tmp, ll) where
	v_inputSum = calcNeuron ll (weights n)
	v_state = sigmoidFunction v_inputSum
	updated = updateNeuron n (v_inputSum) (v_state) (weights n)
	tmp = x ++ [updated]

-- ----------------------