[Haskell-cafe] indexed writer monad

Doug McIlroy doug at cs.dartmouth.edu
Thu Apr 9 13:37:18 UTC 2015

I infer from the following dialog that ghci nontransparently caches
knowledge about the contents of the library. This is doubtless
helpful for the flurry of imports that a single "load" or interactive
"import" may cause. But the time saved by caching from one such
top-level action to the next is probably imperceptible. The hours
wasted in the present instance and others like it (the very quick
response on cafe suggests that it's not unusual) probably outweigh
all the milliseconds that the cache normally saves.

Non-transparent caching is inherently evil. While the risk may
be justifiable in some cases (e.g. stdio buffers in C), it is very
questionable at top level in ghci. Doesn't this warrant a ticket?


>> I install the indexed package by using cabal
>> Cabal install indexed
>> https://hackage.haskell.org/package/indexed
>> Seemed to do something.
>> Then I want to use that package...
>>> import Control.Monad.Indexed
>> Boom...unknown...
> Possibly silly question but... did you restart `ghci` after installing indexed?


Maybe this Haskell lark isnt as hard as I thought....

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