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fmap :: Functor f => (a -> b) -> f a -> f bLambdaHack Game.LambdaHack.Core.Prelude fmap is used to apply a function of type (a -> b) to a value of type f a, where f is a functor, to produce a value of type f b. Note that for any type constructor with more than one parameter (e.g., Either), only the last type parameter can be modified with fmap (e.g., b in `Either a b`). Some type constructors with two parameters or more have a Bifunctor instance that allows both the last and the penultimate parameters to be mapped over.
Examples
Convert from a Maybe Int to a Maybe String using show:>>> fmap show Nothing Nothing >>> fmap show (Just 3) Just "3"
Convert from an Either Int Int to an Either Int String using show:>>> fmap show (Left 17) Left 17 >>> fmap show (Right 17) Right "17"
Double each element of a list:>>> fmap (*2) [1,2,3] [2,4,6]
Apply even to the second element of a pair:>>> fmap even (2,2) (2,True)
It may seem surprising that the function is only applied to the last element of the tuple compared to the list example above which applies it to every element in the list. To understand, remember that tuples are type constructors with multiple type parameters: a tuple of 3 elements (a,b,c) can also be written (,,) a b c and its Functor instance is defined for Functor ((,,) a b) (i.e., only the third parameter is free to be mapped over with fmap). It explains why fmap can be used with tuples containing values of different types as in the following example:>>> fmap even ("hello", 1.0, 4) ("hello",1.0,True)foldMap :: (Foldable t, Monoid m) => (a -> m) -> t a -> mLambdaHack Game.LambdaHack.Core.Prelude Map each element of the structure into a monoid, and combine the results with (<>). This fold is right-associative and lazy in the accumulator. For strict left-associative folds consider foldMap' instead.
Examples
Basic usage:>>> foldMap Sum [1, 3, 5] Sum {getSum = 9}>>> foldMap Product [1, 3, 5] Product {getProduct = 15}>>> foldMap (replicate 3) [1, 2, 3] [1,1,1,2,2,2,3,3,3]
When a Monoid's (<>) is lazy in its second argument, foldMap can return a result even from an unbounded structure. For example, lazy accumulation enables Data.ByteString.Builder to efficiently serialise large data structures and produce the output incrementally:>>> import qualified Data.ByteString.Lazy as L >>> import qualified Data.ByteString.Builder as B >>> let bld :: Int -> B.Builder; bld i = B.intDec i <> B.word8 0x20 >>> let lbs = B.toLazyByteString $ foldMap bld [0..] >>> L.take 64 lbs "0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24"
oimapVector :: ContentData a -> (ContentId a -> a -> b) -> Vector bLambdaHack Game.LambdaHack.Definition.ContentData No documentation available.
omapVector :: ContentData a -> (a -> b) -> Vector bLambdaHack Game.LambdaHack.Definition.ContentData No documentation available.
sknowMap :: ServerOptions -> BoolLambdaHack Game.LambdaHack.Server No documentation available.
buildTileMap :: COps -> Cave -> Rnd TileMapLambdaHack Game.LambdaHack.Server.DungeonGen No documentation available.
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LambdaHack Game.LambdaHack.Server.DungeonGen No documentation available.
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LambdaHack Game.LambdaHack.Server.DungeonGen.Cave tile kinds in the cave
type
TileMapEM = EnumMap Point ContentId TileKindLambdaHack Game.LambdaHack.Server.DungeonGen.Place The map of tile kinds in a place (and generally anywhere in a cave). The map is sparse. The default tile that eventually fills the empty spaces is specified in the cave kind specification with cdefTile.
buildFenceMap :: ContentId TileKind -> ContentId TileKind -> Area -> TileMapEMLambdaHack Game.LambdaHack.Server.DungeonGen.Place Construct a fence around an area, with the given tile kind. Corners have a different kind, e.g., to avoid putting doors there.