1 files changed, 94 insertions, 0 deletions
diff --git a/src/Error.hs b/src/Error.hs
new file mode 100644
index 0000000..0260aa1
--- /dev/null
+++ b/src/Error.hs
@@ -0,0 +1,94 @@
+-- MIT License, Copyright (c) 2022 Marvin Borner
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module Error where
+
+import           Data.List                      ( intercalate )
+import           Text.Megaparsec
+
+import           Helper
+
+errPrefix :: String
+errPrefix = "\ESC[101m\ESC[30mERROR\ESC[0m "
+
+okPrefix :: String
+okPrefix = "\ESC[102m\ESC[30m OK \ESC[0m "
+
+data Error = SyntaxError String
+           | UndefinedIdentifier Identifier
+           | UnmatchedMixfix [MixfixIdentifierKind] [Mixfix]
+           | InvalidIndex Int
+           | FailedTest Expression Expression Expression Expression
+           | PassedTest Expression Expression
+           | ContextualError Error Context
+           | SuggestSolution Error String
+           | ImportError String
+           | OptimizerError String
+
+instance Show Error where
+  show (ContextualError err ctx) = show err <> "\n" <> printContext ctx
+  show (SuggestSolution err sol) =
+    show err <> "\n\ESC[102m\ESC[30msuggestion\ESC[0m Perhaps you meant " <> sol
+  show (SyntaxError err) =
+    errPrefix <> "invalid syntax\n\ESC[105m\ESC[30mnear\ESC[0m " <> err
+  show (UndefinedIdentifier ident) =
+    errPrefix <> "undefined identifier " <> show ident
+  show (UnmatchedMixfix ks ms) =
+    errPrefix
+      <> "couldn't find matching mixfix for "
+      <> intercalate "" (map show ks)
+      <> "\n\ESC[105m\ESC[30mnear\ESC[0m "
+      <> unwords (map show ms)
+  show (InvalidIndex err) = errPrefix <> "invalid index " <> show err
+  show (PassedTest exp1 exp2) =
+    okPrefix <> "test passed: " <> show exp1 <> " = " <> show exp2
+  show (FailedTest exp1 exp2 red1 red2) =
+    errPrefix
+      <> "test failed: "
+      <> show exp1
+      <> " = "
+      <> show exp2
+      <> "\n      reduced to "
+      <> show red1
+      <> " = "
+      <> show red2
+  show (ImportError    path) = errPrefix <> "invalid import " <> show path
+  show (OptimizerError msg ) = errPrefix <> "optimizer failed: " <> msg
+
+type Failable = Either Error
+
+-- Modified from megaparsec's errorBundlePretty
+printBundle
+  :: forall s e
+   . (VisualStream s, TraversableStream s, ShowErrorComponent e)
+  => ParseErrorBundle s e
+  -> String
+printBundle ParseErrorBundle {..} =
+  let (r, _) = foldl f (id, bundlePosState) bundleErrors in drop 1 (r "")
+ where
+  f :: (ShowS, PosState s) -> ParseError s e -> (ShowS, PosState s)
+  f (o, !pst) e = (o . (outChunk ++), pst')
+   where
+    (msline, pst') = reachOffset (errorOffset e) pst
+    epos           = pstateSourcePos pst'
+    outChunk       = "\n\n" <> offendingLine <> init (parseErrorTextPretty e)
+    offendingLine  = case msline of
+      Nothing -> ""
+      Just sline ->
+        let pointer    = "^"
+            rpadding   = replicate rpshift ' '
+            rpshift    = unPos (sourceColumn epos) - 2
+            lineNumber = (show . unPos . sourceLine) epos
+            padding    = replicate (length lineNumber + 1) ' '
+        in  padding
+              <> "|\n"
+              <> "  | "
+              <> sline
+              <> "\n"
+              <> padding
+              <> "|  "
+              <> rpadding
+              <> pointer
+              <> "\n"