Data.Grib

The GRIB Monad

type GribIO = ReaderT GribEnv IO

The GribIO monad is a ReaderT monad transformer over the IO monad with a GribEnv environment.

runGribIO

Arguments

:: FilePath

a path to a GRIB file

-> GribIO a

an action to take on each GRIB message in the file

-> IO [a]

the results of the actions

Run an action on each GRIB message in a file and collect the results.

This operation may fail with:

• any IOError raised by openBinaryCFile;
• any GribError raised by gribHandleNewFromFile; or
• any other exception raised by the given GribIO action.

runGribIO_ :: FilePath -> GribIO a -> IO ()

Like runGribIO, but discard the results.

skipMessage :: GribIO a

Skip the current GRIB message. No result will be put in the output list of runGribIO for this message.

skipMessageIf

Arguments

:: (a -> Bool)

a predicate that will be given the result of the action

-> GribIO a

an action to perform

-> GribIO a

Skip the current GRIB message if the predicate is true. No result will be put in the output list of runGribIO in this case.

skipMessageIf_ :: (a -> Bool) -> GribIO a -> GribIO ()

Like skipMessageIf, but discard the result of the action.

Examples

Sum all grid points of the first vertical level in a GRIB message:

runGribIO "test/stage/test_uuid.grib2" $ do
  skipMessageIf_ (/= 1) $ getLong "topLevel"
  fmap sum getValues

Get values

These operations may fail with:

• isGribException GribNotFound if the key is missing.

getDouble :: Key -> GribIO Double

Get the value for a key as a float.

getLong :: Key -> GribIO Int

Get the value for a key as an integer.

getString :: Key -> GribIO String

Get the value for a key as a string.

getValues :: GribIO [Double]

Get the data values of the GRIB message as floats.

Set values

These operations may fail with:

• isGribException GribNotFound if the key is missing; or
• isGribException GribReadOnly if the key is read-only.

setDouble :: Key -> Double -> GribIO ()

Set the value of a key from a float.

setLong :: Key -> Int -> GribIO ()

Set the value of a key from an integer.

setString :: Key -> String -> GribIO ()

Set the value of a key from a string.

setValues :: [Double] -> GribIO ()

Set the values of the GRIB message from floats.

Utilities

getFilename :: GribIO FilePath

Return the name of the file being read.

getIndex :: GribIO Int

Return the zero-based index of the current message in the file.

getHandle :: GribIO GribHandle

Return the current GribHandle for use with the Raw GRIB API bindings.

liftIO :: MonadIO m => forall a. IO a -> m a

Lift a computation from the IO monad.

Auxiliary types

data GribEnv

The reader environment of GribIO containing the current filename, a GribHandle, and its index in the file.

data SkipMessage

If this exception is raised in GribIO, the message will be discarded. Normally, you simply call skipMessage instead of throwing this exception manually.

Instances

Show SkipMessage

Exception SkipMessage