FetchGit.hs

data UpdateSource = VersionSet{ versionExpr :: NExprLoc
                              , sources     :: [UpdateSource]
                              }
                  | FetchGit{ args    :: FetchGitArgs
                            , sources :: [UpdateSource]
                            }

-- This is the 'para' function from the 'recursion-schemes' package
-- I've made the type signature specific to NixExprLoc
para :: (NixExprLocF (NixExprLoc, a) -> a) -> NixExprLoc -> a

f :: NExprLocF (NExprLoc, [UpdateSource]) -> [UpdateSource]
f e = let -- Get all the sub-sources for this expression
          -- This expression has for its subexpressions tuples of type
          -- (NixExprLoc, [UpdateSource]). The first element of this tuple is
          -- the actual subexpression, the second element is the list of
          -- 'UpdateSource's calculated by 'para' further down the tree.
          --
          -- first convert this expression to a list of type
          -- [(NExprLoc, [UpdateSource])] using 'toList' from the 'Foldable'
          -- type class. Then map 'snd' over each element to get the list of
          -- type [UpdateSource] for each element. Finally concatenate all
          -- these lists into one larger list with elements of type
          -- UpdateSource
          subs = concat . map snd . toList $ e
      in case e of
          -- If this is a call to 'fetchgit' then extract the arguments
          CallToFetchGit -> [FetchGit{ args = extractFetchGitArgs (fst <$> e)
                                     , sources = subs
                                     }]
          -- If this is an attr set with a version attribute, remember where
          -- the version attribute was and set the sub sources
          AttrSetWithVersion -> [VersionSet{ versionExpr = extractVersionAttr
                                           , sources = subs
                                           }]
          -- If this is something else, just forward the sub sources
          _somethingUninteresting -> subs