From b1402e8bd6a68a891b00a214d6cf184d66defe19 Mon Sep 17 00:00:00 2001
From: aarne <unknown>
Date: Mon, 22 Sep 2003 13:16:55 +0000
Subject: Founding the newly structured GF2.0 cvs archive.

---
 src/GF/Grammar/PatternMatch.hs | 98 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 src/GF/Grammar/PatternMatch.hs

(limited to 'src/GF/Grammar/PatternMatch.hs')

diff --git a/src/GF/Grammar/PatternMatch.hs b/src/GF/Grammar/PatternMatch.hs
new file mode 100644
index 000000000..2ca8b21de
--- /dev/null
+++ b/src/GF/Grammar/PatternMatch.hs
@@ -0,0 +1,98 @@
+module PatternMatch where
+
+import Operations
+import Grammar
+import Ident
+import Macros
+import PrGrammar
+
+import List
+import Monad
+
+-- pattern matching for both concrete and abstract syntax. AR -- 16/6/2003
+
+
+matchPattern :: [(Patt,Term)] -> Term -> Err (Term, Substitution)
+matchPattern pts term = 
+  errIn ("trying patterns" +++ unwords (intersperse "," (map (prt . fst) pts))) $
+  findMatch [([p],t) | (p,t) <- pts] [term]
+
+testOvershadow :: [Patt] -> [Term] -> Err [Patt]
+testOvershadow pts vs = do
+  let numpts = zip pts [0..]
+  let cases  = [(p,EInt i) | (p,i) <- numpts]
+  ts <- mapM (liftM fst . matchPattern cases) vs
+  return $ [p | (p,i) <- numpts, notElem i [i | EInt i <- ts] ]
+
+findMatch :: [([Patt],Term)] -> [Term] -> Err (Term, Substitution)
+findMatch cases terms = case cases of
+   [] -> Bad $"no applicable case for" +++ unwords (intersperse "," (map prt terms))
+   (patts,_):_ | length patts /= length terms -> 
+       Bad ("wrong number of args for patterns :" +++ 
+            unwords (map prt patts) +++ "cannot take" +++ unwords (map prt terms))
+   (patts,val):cc -> case mapM tryMatch (zip patts terms) of
+       Ok substs -> return (val, concat substs)
+       _         -> findMatch cc terms
+
+tryMatch :: (Patt, Term) -> Err [(Ident, Term)]
+tryMatch (p,t) = do 
+  t' <- termForm t
+  trym p t'
+ where
+  trym p t' =
+    case (p,t') of
+      (PV IW, _) | isInConstantForm t -> return [] -- optimization with wildcard
+      (PV x,  _) | isInConstantForm t -> return [(x,t)]
+      (PString s, ([],K i,[])) | s==i -> return []
+      (PInt s, ([],EInt i,[])) | s==i -> return []
+      (PC p pp, ([], Con f, tt)) | 
+            p `eqStrIdent` f && length pp == length tt ->
+         do matches <- mapM tryMatch (zip pp tt)
+            return (concat matches)
+      (PP q p pp, ([], QC r f, tt)) | 
+            q `eqStrIdent` r && p `eqStrIdent` f && length pp == length tt ->
+         do matches <- mapM tryMatch (zip pp tt)
+            return (concat matches)
+      ---- hack for AppPredef bug
+      (PP q p pp, ([], Q r f, tt)) | 
+            q `eqStrIdent` r && p `eqStrIdent` f && length pp == length tt ->
+         do matches <- mapM tryMatch (zip pp tt)
+            return (concat matches)
+
+      (PR r, ([],R r',[])) |
+            all (`elem` map fst r') (map fst r) ->
+         do matches <- mapM tryMatch 
+                            [(p,snd a) | (l,p) <- r, let Just a = lookup l r']
+            return (concat matches)
+      (PT _ p',_) -> trym p' t'
+      (_, ([],Alias _ _ d,[])) -> tryMatch (p,d)
+      _ -> prtBad "no match in case expr for" t
+  
+isInConstantForm :: Term -> Bool
+isInConstantForm trm = case trm of
+    Cn _     -> True
+    Con _    -> True
+    Q _ _    -> True
+    QC _ _   -> True
+    Abs _ _  -> True
+    App c a  -> isInConstantForm c && isInConstantForm a
+    R r      -> all (isInConstantForm . snd . snd) r
+    Alias _ _ t -> isInConstantForm t
+    _       -> False ---- isInArgVarForm trm
+
+varsOfPatt :: Patt -> [Ident]
+varsOfPatt p = case p of
+  PV x -> [x | not (isWildIdent x)]
+  PC _ ps -> concat $ map varsOfPatt ps
+  PP _ _ ps -> concat $ map varsOfPatt ps
+  PR r    -> concat $ map (varsOfPatt . snd) r
+  PT _ q -> varsOfPatt q
+  _ -> []
+
+-- to search matching parameter combinations in tables
+isMatchingForms :: [Patt] -> [Term] -> Bool
+isMatchingForms ps ts = all match (zip ps ts') where
+  match (PC c cs, (Cn d, ds)) = c == d && isMatchingForms cs ds
+  match _ = True
+  ts' = map appForm ts
+
-- 
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