pgf-service: add Jordis transfer function for OpenMath LaTeX output

src/server/transfer/Fold.hs

@@ -0,0 +1,26 @@
+module Fold where
+import PGF
+import Data.Map as M (lookup, fromList)
+
+--import Debug.Trace
+
+
+foldable = fromList [(mkCId c, mkCId ("bin_" ++ c)) | c <- ops]
+  where ops = words "plus times and or xor cartesian_product intersect union"
+
+fold :: Tree -> Tree
+fold t =
+  case unApp t of
+    Just (i,[x])  ->
+        case M.lookup i foldable of
+	        Just j -> appFold j x
+	        _      -> mkApp i [fold x]
+    Just (i,xs)   -> mkApp i $ map fold xs
+    _             -> t
+
+appFold :: CId -> Tree -> Tree
+appFold j t = 
+  case unApp t of
+    Just (i,[t,ts]) | isPre i "Cons"  -> mkApp j [fold t, appFold j ts]
+    Just (i,[t,s])  | isPre i "Base"  -> mkApp j [fold t, fold s]
+  where isPre i s = take 4 (show i) == s