Tracing simplifier

1 files changed, 80 insertions, 0 deletions

diff --git a/src/Simplify/TH.hs b/src/Simplify/TH.hs
new file mode 100644
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--- /dev/null
+++ b/src/Simplify/TH.hs
@@ -0,0 +1,80 @@
+{-# LANGUAGE TemplateHaskellQuotes #-}
+module Simplify.TH (simprec) where
+
+import Data.Bifunctor (first)
+import Data.Char
+import Data.List (foldl1')
+import Language.Haskell.TH
+import Language.Haskell.TH.Quote
+import Text.ParserCombinators.ReadP
+
+
+-- [simprec| EPair ext *a *b |]
+-- ~>
+-- do a' <- within (\a' -> EPair ext a' b) (simplify' a)
+--    b' <- within (\b' -> EPair ext a' b') (simplify' b)
+--    pure (EPair ext a' b')
+
+simprec :: QuasiQuoter
+simprec = QuasiQuoter
+  { quoteDec = \_ -> fail "simprec used outside of expression context"
+  , quoteType = \_ -> fail "simprec used outside of expression context"
+  , quoteExp = handler
+  , quotePat = \_ -> fail "simprec used outside of expression context"
+  }
+
+handler :: String -> Q Exp
+handler str =
+  case readP_to_S pTemplate str of
+    [(template, "")] -> generate template
+    _:_:_ -> fail "simprec: template grammar ambiguous"
+    _ -> fail "simprec: could not parse template"
+
+generate :: Template -> Q Exp
+generate (Template topitems) =
+  let takePrefix (Plain x : xs) = first (x:) (takePrefix xs)
+      takePrefix xs = ([], xs)
+
+      itemVar "" = error "simprec: empty item name?"
+      itemVar name@(c:_) | isLower c = VarE (mkName name)
+                         | isUpper c = ConE (mkName name)
+                         | otherwise = error "simprec: non-letter item name?"
+
+      loop :: Exp -> [Item] -> Q [Stmt]
+      loop yet [] = return [NoBindS (VarE 'pure `AppE` yet)]
+      loop yet (Plain x : xs) = loop (yet `AppE` itemVar x) xs
+      loop yet (Recurse x : xs) = do
+        primeName <- newName (x ++ "'")
+        let appPrePrime e (Plain y) = e `AppE` itemVar y
+            appPrePrime e (Recurse y) = e `AppE` itemVar y
+        let stmt = BindS (VarP primeName) $
+                     VarE (mkName "within")
+                     `AppE` LamE [VarP primeName] (foldl' appPrePrime (yet `AppE` VarE primeName) xs)
+                     `AppE` (VarE (mkName "simplify'") `AppE` VarE (mkName x))
+        stmts <- loop (yet `AppE` VarE primeName) xs
+        return (stmt : stmts)
+
+      (prefix, items') = takePrefix topitems
+  in DoE Nothing <$> loop (foldl1' AppE (map itemVar prefix)) items'
+
+data Template = Template [Item]
+  deriving (Show)
+
+data Item = Plain String | Recurse String
+  deriving (Show)
+
+pTemplate :: ReadP Template
+pTemplate = do
+  items <- many (skipSpaces >> pItem)
+  skipSpaces
+  eof
+  return (Template items)
+
+pItem :: ReadP Item
+pItem = (char '*' >> Recurse <$> pName) +++ (Plain <$> pName)
+
+pName :: ReadP String
+pName = do
+  c1 <- satisfy (\c -> isAlpha c || c == '_')
+  cs <- munch (\c -> isAlphaNum c || c `elem` "_'")
+  return (c1:cs)