Commit 13f359ca authored by Edward Z. Yang's avatar Edward Z. Yang Committed by Edward Z. Yang
Browse files

Documentation for CondTree and CondBranch.


Signed-off-by: default avatarEdward Z. Yang <ezyang@cs.stanford.edu>
parent 4856dbb1
......@@ -23,6 +23,31 @@ import Distribution.Compat.Prelude
import Distribution.Types.Condition
-- | A 'CondTree' is used to represent the conditional structure of
-- a Cabal file, reflecting a syntax element subject to constraints,
-- and then any number of sub-elements which may be enabled subject
-- to some condition. Both @a@ and @c@ are usually 'Monoid's.
--
-- To be more concrete, consider the following fragment of a @Cabal@
-- file:
--
-- @
-- build-depends: base >= 4.0
-- if flag(extra)
-- build-depends: base >= 4.2
-- @
--
-- One way to represent this is to have @'CondTree' 'ConfVar'
-- ['Dependency'] 'BuildInfo'@. Here, 'condTreeData' represents
-- the actual fields which are not behind any conditional, while
-- 'condTreeComponents' recursively records any further fields
-- which are behind a conditional. 'condTreeConstraints' records
-- the constraints (in this case, @base >= 4.0@) which would
-- be applied if you use this syntax; in general, this is
-- derived off of 'targetBuildInfo' (perhaps a good refactoring
-- would be to convert this into an opaque type, with a smart
-- constructor that pre-computes the dependencies.)
--
data CondTree v c a = CondNode
{ condTreeData :: a
, condTreeConstraints :: c
......@@ -32,6 +57,10 @@ data CondTree v c a = CondNode
instance (Binary v, Binary c, Binary a) => Binary (CondTree v c a)
-- | A 'CondBranch' represents a conditional branch, e.g., @if
-- flag(foo)@ on some syntax @a@. It also has an optional false
-- branch.
--
data CondBranch v c a = CondBranch
{ condBranchCondition :: Condition v
, condBranchIfTrue :: CondTree v c a
......
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