added the minimal Haskell API for storing expressions/triples in the semantic graph

src/runtime/haskell-bind/PGF2/Expr.hsc

@@ -0,0 +1,138 @@
+{-# LANGUAGE ExistentialQuantification #-}
+#include <pgf/pgf.h>
+
+module PGF2.Expr where
+
+import Foreign
+import Foreign.C
+import qualified Text.PrettyPrint as PP
+import PGF2.FFI
+
+type CId = String
+
+ppCId = PP.text
+wildCId = "_" :: CId
+
+type Cat = String -- ^ Name of syntactic category
+type Fun = String -- ^ Name of function
+
+-----------------------------------------------------------------------------
+-- Expressions
+
+-- The C structure for the expression may point to other structures
+-- which are allocated from other pools. In order to ensure that
+-- they are not released prematurely we use the exprMaster to
+-- store references to other Haskell objects
+
+data Expr = forall a . Expr {expr :: PgfExpr, exprMaster :: a}
+
+instance Show Expr where
+  show = showExpr
+
+mkApp :: Fun -> [Expr] -> Expr
+mkApp fun args =
+  unsafePerformIO $
+    withCString fun $ \cfun ->
+    allocaBytes ((#size PgfApplication) + len * sizeOf (undefined :: PgfExpr)) $ \papp -> do
+      (#poke PgfApplication, fun) papp cfun
+      (#poke PgfApplication, n_args) papp len
+      pokeArray (papp `plusPtr` (#offset PgfApplication, args)) (map expr args)
+      exprPl <- gu_new_pool
+      c_expr <- pgf_expr_apply papp exprPl
+      exprFPl <- newForeignPtr gu_pool_finalizer exprPl
+      return (Expr c_expr (exprFPl,args))
+  where
+    len = length args
+
+unApp :: Expr -> Maybe (Fun,[Expr])
+unApp (Expr expr master) =
+  unsafePerformIO $
+    withGuPool $ \pl -> do
+      appl <- pgf_expr_unapply expr pl
+      if appl == nullPtr
+        then return Nothing
+        else do 
+           fun <- peekCString =<< (#peek PgfApplication, fun) appl
+           arity <- (#peek PgfApplication, n_args) appl :: IO CInt 
+           c_args <- peekArray (fromIntegral arity) (appl `plusPtr` (#offset PgfApplication, args))
+           return $ Just (fun, [Expr c_arg master | c_arg <- c_args])
+
+mkStr :: String -> Expr
+mkStr str =
+  unsafePerformIO $
+    withCString str $ \cstr -> do
+      exprPl <- gu_new_pool
+      c_expr <- pgf_expr_string cstr exprPl
+      exprFPl <- newForeignPtr gu_pool_finalizer exprPl
+      return (Expr c_expr exprFPl)
+
+readExpr :: String -> Maybe Expr
+readExpr str =
+  unsafePerformIO $
+    do exprPl <- gu_new_pool
+       withGuPool $ \tmpPl ->
+         withCString str $ \c_str ->
+           do guin <- gu_string_in c_str tmpPl
+              exn <- gu_new_exn tmpPl
+              c_expr <- pgf_read_expr guin exprPl exn
+              status <- gu_exn_is_raised exn
+              if (not status && c_expr /= nullPtr)
+                then do exprFPl <- newForeignPtr gu_pool_finalizer exprPl
+                        return $ Just (Expr c_expr exprFPl)
+                else do gu_pool_free exprPl
+                        return Nothing
+
+ppExpr :: Int -> Expr -> PP.Doc
+ppExpr d e = ppParens (d>0) (PP.text (showExpr e)) -- just a quick hack !!!
+
+showExpr :: Expr -> String
+showExpr e = 
+  unsafePerformIO $
+    withGuPool $ \tmpPl ->
+      do (sb,out) <- newOut tmpPl
+         let printCtxt = nullPtr
+         exn <- gu_new_exn tmpPl
+         pgf_print_expr (expr e) printCtxt 1 out exn
+         s <- gu_string_buf_freeze sb tmpPl
+         peekCString s
+
+
+-----------------------------------------------------------------------------
+-- Types
+
+data Type =
+   DTyp [Hypo] CId [Expr]
+  deriving Show
+
+data BindType = 
+    Explicit
+  | Implicit
+  deriving Show
+
+-- | 'Hypo' represents a hypothesis in a type i.e. in the type A -> B, A is the hypothesis
+type Hypo = (BindType,CId,Type)
+
+-- | renders type as 'String'.
+showType :: Type -> String
+showType = PP.render . ppType 0
+
+ppType :: Int -> Type -> PP.Doc
+ppType d (DTyp hyps cat args)
+  | null hyps = ppRes cat args
+  | otherwise = let hdocs = map (ppHypo 1) hyps
+                in ppParens (d > 0) (foldr (\hdoc doc -> hdoc PP.<+> PP.text "->" PP.<+> doc) (ppRes cat args) hdocs)
+  where
+    ppRes cat es
+      | null es   = ppCId cat
+      | otherwise = ppParens (d > 3) (ppCId cat PP.<+> PP.hsep (map (ppExpr 4) es))
+
+ppHypo :: Int -> (BindType,CId,Type) -> PP.Doc
+ppHypo d (Explicit,x,typ) =
+    if x == wildCId
+    then ppType d typ
+    else PP.parens (ppCId x PP.<+> PP.char ':' PP.<+> ppType 0 typ)
+ppHypo d (Implicit,x,typ) =
+    PP.parens (PP.braces (ppCId x) PP.<+> PP.char ':' PP.<+> ppType 0 typ)
+
+ppParens True  = PP.parens
+ppParens False = id