feat(haskell): Interaction Tree IO

oops, now we have purely modelled IO 🤷

test/Spec.hs

@@ -8,10 +8,12 @@ import REPL
 import Research
 import Wire
 import ContentStore
+import IODriver
 
 import Control.Exception      (evaluate, try, SomeException)
 import Control.Monad         (forM_)
 import Control.Monad.IO.Class (liftIO)
+import System.IO.Temp         (withSystemTempDirectory)
 import Data.Bits              (xor)
 import Data.Char              (digitToInt)
 import Data.List              (isInfixOf)
@@ -51,6 +53,7 @@ tests = testGroup "Tricu Tests"
   , wireTests
   , tricuReaderTests
   , byteListUtilities
+  , ioDriverTests
   ]
 
 lexer :: TestTree
@@ -1252,3 +1255,58 @@ byteListUtilities = testGroup "Byte List Utility Tests"
       let env = evalTricu library (parseTricu input)
       result env @?= falseT
   ]
+
+-- --------------------------------------------------------------------------
+-- IO driver tests
+-- --------------------------------------------------------------------------
+
+ioDriverTests :: TestTree
+ioDriverTests = testGroup "IO driver tests"
+  [ testCase "readFile through onReadFile returns file contents" $
+      withSystemTempDirectory "tricu-io-read" $ \dir -> do
+        let sourcePath = dir ++ "/input.txt"
+        writeFile sourcePath "abc123"
+        final <- runIOSource $
+          unlines
+            [ "main = io (onReadFile \"" ++ sourcePath ++ "\""
+            , "  (err rest : pure \"read failed\")"
+            , "  (contents rest : pure contents))"
+            ]
+        final @?= ofString "abc123"
+
+  , testCase "readFile error path returns explicit error branch" $
+      withSystemTempDirectory "tricu-io-read-missing" $ \dir -> do
+        let sourcePath = dir ++ "/missing.txt"
+        final <- runIOSource $
+          unlines
+            [ "main = io (onReadFile \"" ++ sourcePath ++ "\""
+            , "  (err rest : pure \"read failed\")"
+            , "  (contents rest : pure contents))"
+            ]
+        final @?= ofString "read failed"
+
+  , testCase "chains multiple readFile actions through Result-aware helper" $
+      withSystemTempDirectory "tricu-io-chain" $ \dir -> do
+        let firstPath = dir ++ "/first.txt"
+            secondPath = dir ++ "/second.txt"
+        writeFile firstPath "abc"
+        writeFile secondPath "def"
+        final <- runIOSource $
+          unlines
+            [ "main = io (onReadFile \"" ++ firstPath ++ "\""
+            , "  (err rest : pure \"first read failed\")"
+            , "  (first rest : onReadFile \"" ++ secondPath ++ "\""
+            , "    (err rest : pure \"second read failed\")"
+            , "    (second rest : pure (append first second))))"
+            ]
+        final @?= ofString "abcdef"
+  ]
+
+runIOSource :: String -> IO T
+runIOSource source = do
+  ioEnv <- evaluateFile "./lib/io.tri"
+  env <- evalTricuWithStore Nothing ioEnv (parseTricu source)
+  case checkIOSentinel (mainResult env) of
+    Right (1, action) -> runIO defaultPerms action
+    Right (v, _)      -> assertFailure ("Unsupported IO ABI version: " ++ show v)
+    Left err          -> assertFailure ("Expected IO sentinel: " ++ err)