GHC.Core.Opt.Monad

Lift a computation from the IO monad. This allows us to run IO computations in any monadic stack, so long as it supports these kinds of operations (i.e. IO is the base monad for the stack).

Example

import Control.Monad.Trans.State -- from the "transformers" library

printState :: Show s => StateT s IO ()
printState = do
  state <- get
  liftIO $ print state

Had we omitted liftIO, we would have ended up with this error:

• Couldn't match type ‘IO’ with ‘StateT s IO’
 Expected type: StateT s IO ()
   Actual type: IO ()

The important part here is the mismatch between StateT s IO () and IO ().

Luckily, we know of a function that takes an IO a and returns an (m a): liftIO, enabling us to run the program and see the expected results:

> evalStateT printState "hello"
"hello"

> evalStateT printState 3
3

Lift an IO operation into CoreM while consuming its SimplCount

Get all annotations of a given type. This happens lazily, that is no deserialization will take place until the [a] is actually demanded and the [a] can also be empty (the UniqFM is not filtered).

This should be done once at the start of a Core-to-Core pass that uses annotations.

See Note [Annotations]

Get at most one annotation of a given type per annotatable item.

Output a message to the screen

Output a String message to the screen

Output an error to the screen. Does not cause the compiler to die.

Output a fatal error to the screen. Does not cause the compiler to die.

Output a fatal error to the screen. Does not cause the compiler to die.

Outputs a debugging message at verbosity level of -v or higher

Output a string debugging message at verbosity level of -v or higher