readIO package:base

The readIO function is similar to read except that it signals parse failure to the IO monad instead of terminating the program. This operation may fail with:

• isUserError if there is no unambiguous parse.

Examples

>>> fmap (+ 1) (readIO "1")
2

>>> readIO "not quite ()" :: IO ()
*** Exception: user error (Prelude.readIO: no parse)

Read the value of an IORef. Beware that the CPU executing a thread can reorder reads or writes to independent locations. See Data.IORef#memmodel for more details.

Read a value from an IOArray

Atomically read the contents of the IOPort. If the IOPort is currently empty, readIOPort will wait until it is full. After a readIOPort, the IOPort is left empty. There is one important property of readIOPort:

• Only a single threads can be blocked on an IOPort.

Read a value from an IOArray