From 7a64aefac2efb718f58e299a12fa5fd895c1b657 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke_lau@icloud.com>
Date: Sun, 10 Mar 2019 15:13:34 +0000
Subject: [PATCH] Add basic error handling

---
 Main.hs | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/Main.hs b/Main.hs
index f721911..29592b1 100644
--- a/Main.hs
+++ b/Main.hs
@@ -8,6 +8,7 @@ import qualified Data.Text.Lazy.IO as Text
 import           Data.String
 import Foreign.Ptr
 import System.IO
+import           System.Exit
 import LLVM.Context
 import LLVM.ExecutionEngine
 import LLVM.Module
@@ -20,14 +21,19 @@ import LLVM.AST.Operand
 import LLVM.AST.Type as Type
 import LLVM.Pretty
 import           Control.Monad
+import           Control.Monad.Trans.Class
+
+type ModuleBuilderE = ModuleBuilderT (Either String)
 
 foreign import ccall "dynamic" exprFun :: FunPtr (IO Float) -> IO Float
 
 main :: IO ()
 main = do
   AST.Program asts <- read <$> getContents
-  let mdl = buildModule "main" $ mapM buildAST asts
-  withContext $ \ctx ->
+  let eitherMdl = buildModuleT "main" $ mapM buildAST asts
+  case eitherMdl of
+    Left err -> die err
+    Right mdl -> withContext $ \ctx ->
       withMCJIT ctx Nothing Nothing Nothing Nothing $ \mcjit ->
         withModuleFromAST ctx mdl $ \mdl' ->
           withPassManager defaultCuratedPassSetSpec $ \pm -> do
@@ -38,19 +44,21 @@ main = do
               let f' = castFunPtr f :: FunPtr (IO Float)
               exprFun f' >>= print
 
-buildAST :: AST.AST -> ModuleBuilder Operand
+buildAST :: AST.AST -> ModuleBuilderE Operand
 buildAST (AST.Function nameStr paramStrs body) = do
-  let name = fromString nameStr
-  function name params float $ \binds -> do
+  let n = fromString nameStr
+  function n params float $ \binds -> do
     let bindMap = Map.fromList (zip paramStrs binds)
     buildExpr bindMap body >>= ret
   where params = zip (repeat float) (map fromString paramStrs)
 buildAST (AST.Eval e) =
   function "expr" [] float $ \_ -> buildExpr mempty e >>= ret
 
-buildExpr :: Map.Map String Operand -> AST.Expr -> IRBuilderT ModuleBuilder Operand
+buildExpr :: Map.Map String Operand -> AST.Expr -> IRBuilderT ModuleBuilderE Operand
 buildExpr _ (AST.Num a) = pure $ ConstantOperand (Float (Single a))
-buildExpr binds (AST.Var name) = pure $ binds Map.! name
+buildExpr binds (AST.Var n) = case binds Map.!? n of
+  Just x -> pure x
+  Nothing -> lift $ lift $ Left $ "'" <> n <> "' doesn't exist in scope"
 
 buildExpr binds (AST.Call nameStr params) = do
   paramOps <- mapM (buildExpr binds) params
-- 
2.30.2