Add docstrings to Brick.AttrMap

src/Brick/AttrMap.hs

@@ -1,10 +1,18 @@
+-- | This module provides types and functions for managing an attribute
+-- map which maps attribute names ('AttrName') to attributes ('Attr').
+-- This module is designed to be used with the 'OverloadedStrings'
+-- language extension to permit easy construction of 'AttrName' values
+-- and you should also use 'mappend' ('<>') to combine names.
 module Brick.AttrMap
   ( AttrMap
   , AttrName
-  , attrName
+  -- * Construction
   , attrMap
   , forceAttrMap
+  , attrName
+  -- * Finding attributes from names
   , attrMapLookup
+  -- * Manipulating attribute maps
   , setDefault
   , applyAttrMappings
   , mergeWithDefault
@@ -21,6 +29,18 @@ import Data.Default (Default(..))
 
 import Graphics.Vty (Attr(..), MaybeDefault(..))
 
+-- | An attribute name. Attribute names are hierarchical; use 'mappend'
+-- ('<>') to assemble them. Hierachy in an attribute name is used to
+-- represent increasing levels of specificity in referring to the
+-- attribute you want to use for a visual element, with names to the
+-- left being general and names to the right being more specific. For
+-- example:
+--
+-- @
+-- "window" <> "border"
+-- "window" <> "title"
+-- "header" <> "clock" <> "seconds"
+-- @
 data AttrName = AttrName [String]
               deriving (Show, Eq, Ord)
 
@@ -34,6 +54,7 @@ instance Monoid AttrName where
 instance IsString AttrName where
     fromString = AttrName . (:[])
 
+-- | An attribute map which maps 'AttrName' values to 'Attr' values.
 data AttrMap = AttrMap Attr (M.Map AttrName Attr)
              | ForceAttr Attr
              deriving Show
@@ -41,19 +62,64 @@ data AttrMap = AttrMap Attr (M.Map AttrName Attr)
 instance Default AttrMap where
     def = AttrMap def mempty
 
+-- | Create an attribute name from a string.
 attrName :: String -> AttrName
 attrName = AttrName . (:[])
 
-attrMap :: Attr -> [(AttrName, Attr)] -> AttrMap
+-- | Create an attribute map.
+attrMap :: Attr
+        -- ^ The map's default attribute to be returned when a name
+        -- lookup fails, and the attribute that will be merged with
+        -- successful lookups.
+        -> [(AttrName, Attr)]
+        -- ^ The map's initial contents.
+        -> AttrMap
 attrMap theDefault pairs = AttrMap theDefault (M.fromList pairs)
 
+-- | Create an attribute map in which all lookups map to the same
+-- attribute.
 forceAttrMap :: Attr -> AttrMap
 forceAttrMap = ForceAttr
 
+-- | Given an attribute and a map, merge the attribute with the map's
+-- default attribute. If the map is forcing all lookups to a specific
+-- attribute, the forced attribute is returned without merging it with
+-- the one specified here. Otherwise the attribute given here is merged
+-- with the attribute map's default attribute in that any aspect of the
+-- specified attribute that is not provided falls back to the map
+-- default. For example,
+--
+-- @
+-- mergeWithDefault (fg blue) $ attrMap (bg red) []
+-- @
+--
+-- returns
+--
+-- @
+-- blue \`on\` red
+-- @
 mergeWithDefault :: Attr -> AttrMap -> Attr
 mergeWithDefault _ (ForceAttr a) = a
 mergeWithDefault a (AttrMap d _) = combineAttrs d a
 
+-- | Look up the specified attribute name in the map. Map lookups
+-- proceed as follows. If the attribute map is forcing all lookups to a
+-- specific attribute, that attribute is returned. If the attribute name
+-- is empty, the map's default attribute is returned. If the attribute
+-- name is non-empty, very subsequence of names from the specified name
+-- are used to perform a lookup, and the results are combined as in
+-- 'mergeWithDefault', with more specific results taking precedence over
+-- less specific ones.
+--
+-- For example:
+--
+-- @
+-- attrMapLookup ("foo" <> "bar") (attrMap a []) == a
+-- attrMapLookup ("foo" <> "bar") (attrMap (bg blue) [("foo" <> "bar", fg red)]) == red \`on\` blue
+-- attrMapLookup ("foo" <> "bar") (attrMap (bg blue) [("foo" <> "bar", red `on` cyan)]) == red \`on\` cyan
+-- attrMapLookup ("foo" <> "bar") (attrMap (bg blue) [("foo" <> "bar", fg red), ("foo", bg cyan)]) == red \`on\` cyan
+-- attrMapLookup ("foo" <> "bar") (attrMap (bg blue) [("foo", fg red)]) == red \`on\` blue
+-- @
 attrMapLookup :: AttrName -> AttrMap -> Attr
 attrMapLookup _ (ForceAttr a) = a
 attrMapLookup (AttrName []) (AttrMap theDefault _) = theDefault
@@ -61,6 +127,7 @@ attrMapLookup (AttrName ns) (AttrMap theDefault m) =
     let results = catMaybes $ (\n -> M.lookup n m) <$> (AttrName <$> (inits ns))
     in foldl combineAttrs theDefault results
 
+-- | Set the default attribute value in an attribute map.
 setDefault :: Attr -> AttrMap -> AttrMap
 setDefault _ (ForceAttr a) = ForceAttr a
 setDefault newDefault (AttrMap _ m) = AttrMap newDefault m
@@ -76,6 +143,7 @@ combineMDs _ (SetTo v) = SetTo v
 combineMDs (SetTo v) _ = SetTo v
 combineMDs _ v = v
 
+-- | Insert a set of attribute mappings to an attribute map.
 applyAttrMappings :: [(AttrName, Attr)] -> AttrMap -> AttrMap
 applyAttrMappings _ (ForceAttr a) = ForceAttr a
 applyAttrMappings ms (AttrMap d m) = AttrMap d ((M.fromList ms) `M.union` m)