[Haskell-beginners] Question regarding the ListT Monad Transformer
tim at timcowlishaw.co.uk
Wed Aug 4 13:29:24 EDT 2010
I'm trying to get my head around the ListT Monad Transformer, and am
having trouble working out how to use it.
Essentially, I am trying to transform a type of [IO a] to IO [a] I'd
assumed that this might work something like this
Transform [IO a] to ListT IO a
call runListT to transform ListT IO a to IO [a]
..having I'd assumed that this was the correct situation to use a
Monad Transformer, as I'm layering monads around each other.
However, while the second half of the transformation above is catered
for via runListT - I can't seem to work out how to do the first -
namely, to write a function of type [IO a] -> ListT IO a . To be
honest, I'm not entirely sure I've entirely got my head around Monad
Transformers yet - does what I'm describing make any sense at all, and
if so, is there any chance you could point me in the right direction
towards implementing (and hopefully understanding) this?
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