Expression AST and parser

Deleted old AST.hs; old code shall re-appear.

1 files changed, 52 insertions, 0 deletions

diff --git a/src/Language/SimpleShell/Parser.hs b/src/Language/SimpleShell/Parser.hs
new file mode 100644
index 0000000..be78beb
--- /dev/null
+++ b/src/Language/SimpleShell/Parser.hs
@@ -0,0 +1,52 @@
+module Language.SimpleShell.Parser
+  ( Parser
+  , lookupVar
+  , lookupFun
+  , initContext
+  , parseTest'
+  )
+where
+
+
+import Language.SimpleShell.AST.Expr (FunName, VarName)
+import Language.SimpleShell.AST.SimpleType (SimpleType, FunSig)
+
+import Control.Monad.Reader (ask, ReaderT, runReaderT)
+import Data.Map (Map)
+import qualified Data.Map as Map (empty, lookup)
+import Data.Text (Text, unpack)
+import Data.Void (Void)
+import Text.Megaparsec
+
+
+type Parser = ReaderT Context (Parsec Void Text)
+
+data Context = Context
+  { ctxVars :: Map VarName SimpleType
+  , ctxFuns :: Map FunName FunSig
+  }
+
+initContext :: Context
+initContext = Context
+  { ctxVars = Map.empty
+  , ctxFuns = Map.empty
+  }
+
+
+lookupVar :: VarName -> Parser SimpleType
+lookupVar varname = do
+  mt <- Map.lookup varname . ctxVars <$> ask
+  case mt of
+    Just t  -> return t
+    Nothing -> fail $ "Undeclared variable $" ++ unpack varname
+
+lookupFun :: FunName -> Parser FunSig
+lookupFun fname = do
+  msig <- Map.lookup fname . ctxFuns <$> ask
+  case msig of
+    Just sig -> return sig
+    Nothing  -> fail $ "Undefined function " ++ unpack fname
+
+
+parseTest' :: Show a => Parser a -> Text -> IO ()
+parseTest' p = parseTest (runReaderT p initContext)