--in can now refer to files that were located in a repository at some past date. For example, --in="here@{yesterday}"

Git/Ref.hs

@@ -11,6 +11,7 @@ import Common
 import Git
 import Git.Command
 import Git.Sha
+import Git.Types
 
 import Data.Char (chr)
 
@@ -51,6 +52,10 @@ underBase dir r = Ref $ dir ++ "/" ++ show (base r)
 fileRef :: FilePath -> Ref
 fileRef f = Ref $ ":./" ++ f
 
+{- Converts a Ref to refer to the content of the Ref on a given date. -}
+dateRef :: Ref -> RefDate -> Ref
+dateRef (Ref r) (RefDate d) = Ref $ r ++ "@" ++ d
+
 {- A Ref that can be used to refer to a file in the repository as it
  - appears in a given Ref. -}
 fileFromRef :: Ref -> FilePath -> Ref

Git/Types.hs

@@ -57,6 +57,10 @@ type Branch = Ref
 type Sha = Ref
 type Tag = Ref
 
+{- A date in the format described in gitrevisions. Includes the
+ - braces, eg, "{yesterday}" -}
+newtype RefDate = RefDate String
+
 {- Types of objects that can be stored in git. -}
 data ObjectType = BlobObject | CommitObject | TreeObject
 	deriving (Eq)