Brick.AttrMap

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.

Attribute maps work by mapping hierarchical attribute names to attributes and inheriting parent names' attributes when child names specify partial attributes. Hierarchical names are created with mappend:

let n = attrName "parent" <> attrName "child"

Attribute names are mapped to attributes, but some attributes may be partial (specify only a foreground or background color). When attribute name lookups occur, the attribute corresponding to a more specific name ('parent <> child' as above) is sucessively merged with the parent attribute (parent as above) all the way to the "root" of the attribute map, the map's default attribute. In this way, more specific attributes inherit what they don't specify from more general attributes in the same hierarchy. This allows more modularity and less repetition in specifying how elements of your user interface take on different attributes.

Documentation

data AttrMap

An attribute map which maps AttrName values to Attr values.

Instances

Show AttrMap

Methods

showsPrec :: Int -> AttrMap -> ShowS

show :: AttrMap -> String

showList :: [AttrMap] -> ShowS

data AttrName

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"

Instances

Eq AttrName

Methods

(==) :: AttrName -> AttrName -> Bool

(/=) :: AttrName -> AttrName -> Bool

Ord AttrName

Methods

compare :: AttrName -> AttrName -> Ordering

(<) :: AttrName -> AttrName -> Bool

(<=) :: AttrName -> AttrName -> Bool

(>) :: AttrName -> AttrName -> Bool

(>=) :: AttrName -> AttrName -> Bool

max :: AttrName -> AttrName -> AttrName

min :: AttrName -> AttrName -> AttrName

Show AttrName

Methods

showsPrec :: Int -> AttrName -> ShowS

show :: AttrName -> String

showList :: [AttrName] -> ShowS

IsString AttrName

Methods

fromString :: String -> AttrName

Monoid AttrName

Methods

mempty :: AttrName

mappend :: AttrName -> AttrName -> AttrName

mconcat :: [AttrName] -> AttrName

GetAttr AttrName

Methods

getAttr :: AttrName -> RenderM n Attr

Construction

attrMap

Arguments

:: 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

Create an attribute map.

forceAttrMap :: Attr -> AttrMap

Create an attribute map in which all lookups map to the same attribute.

attrName :: String -> AttrName

Create an attribute name from a string.

Finding attributes from names

attrMapLookup :: AttrName -> AttrMap -> Attr

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

Manipulating attribute maps

setDefault :: Attr -> AttrMap -> AttrMap

Set the default attribute value in an attribute map.

applyAttrMappings :: [(AttrName, Attr)] -> AttrMap -> AttrMap

Insert a set of attribute mappings to an attribute map.

mergeWithDefault :: Attr -> AttrMap -> Attr

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

mapAttrName :: AttrName -> AttrName -> AttrMap -> AttrMap

Update an attribute map such that a lookup of ontoName returns the attribute value specified by fromName. This is useful for composite widgets with specific attribute names mapping those names to the sub-widget's expected name when calling that sub-widget's rendering function. See the ProgressBarDemo for an example usage, and overrideAttr for an alternate syntax.

mapAttrNames :: [(AttrName, AttrName)] -> AttrMap -> AttrMap

Map several attributes to return the value associated with an alternate name. Applies mapAttrName across a list of mappings.