reorganize the directories under src, and rescue the JavaScript interpreter from deprecated

src/runtime/haskell/PGF/Tree.hs

@@ -0,0 +1,71 @@
+module PGF.Tree 
+         ( Tree(..),
+           tree2expr, expr2tree,
+           prTree
+         ) where
+
+import PGF.CId
+import PGF.Expr hiding (Tree)
+
+import Data.Char
+import Data.List as List
+import Control.Monad
+import qualified Text.PrettyPrint as PP
+import qualified Text.ParserCombinators.ReadP as RP
+
+-- | The tree is an evaluated expression in the abstract syntax
+-- of the grammar. The type is especially restricted to not
+-- allow unapplied lambda abstractions. The tree is used directly 
+-- from the linearizer and is produced directly from the parser.
+data Tree = 
+   Abs [(BindType,CId)] Tree        -- ^ lambda abstraction. The list of variables is non-empty
+ | Var CId                          -- ^ variable
+ | Fun CId [Tree]                   -- ^ function application
+ | Lit Literal                      -- ^ literal
+ | Meta {-# UNPACK #-} !MetaId      -- ^ meta variable
+  deriving (Eq, Ord)
+
+-----------------------------------------------------
+-- Conversion Expr <-> Tree
+-----------------------------------------------------
+
+-- | Converts a tree to expression. The conversion
+-- is always total, every tree is a valid expression.
+tree2expr :: Tree -> Expr
+tree2expr = tree2expr []
+  where
+    tree2expr ys (Fun x ts) = foldl EApp (EFun x) (List.map (tree2expr ys) ts) 
+    tree2expr ys (Lit l)    = ELit l
+    tree2expr ys (Meta n)   = EMeta n
+    tree2expr ys (Abs xs t) = foldr (\(b,x) e -> EAbs b x e) (tree2expr (List.map snd (reverse xs)++ys) t) xs
+    tree2expr ys (Var x)    = case List.lookup x (zip ys [0..]) of
+                                Just i  -> EVar i
+                                Nothing -> error "unknown variable"
+
+-- | Converts an expression to tree. The conversion is only partial.
+-- Variables and meta variables of function type and beta redexes are not allowed.
+expr2tree :: Expr -> Tree
+expr2tree e = abs [] [] e
+  where
+    abs ys xs (EAbs b x e)    = abs ys ((b,x):xs) e
+    abs ys xs (ETyped e _)    = abs ys xs e
+    abs ys xs e               = case xs of
+                                  [] -> app ys [] e
+                                  xs -> Abs (reverse xs) (app (map snd xs++ys) [] e)
+
+    app xs as (EApp e1 e2)    = app xs ((abs xs [] e2) : as) e1
+    app xs as (ELit l)
+               | List.null as = Lit l
+               | otherwise    = error "literal of function type encountered"
+    app xs as (EMeta n)
+               | List.null as = Meta n
+               | otherwise    = error "meta variables of function type are not allowed in trees"
+    app xs as (EAbs _ x e)    = error "beta redexes are not allowed in trees"
+    app xs as (EVar i)        = Var (xs !! i)
+    app xs as (EFun f)        = Fun f as
+    app xs as (ETyped e _)    = app xs as e
+
+
+prTree :: Tree -> String
+prTree = showExpr [] . tree2expr
+