Helpful library updates

lib/io.tri

@@ -37,6 +37,55 @@ sleep     = ms         : pair 63 ms
 
 thenIO = a b : bind a (_ : b)
 mapIO  = action f : bind action (x : pure (f x))
+void   = action : bind action (_ : pure t)
+
+-- ---------------------------------------------------------------------------
+-- Conditional execution
+-- ---------------------------------------------------------------------------
+
+when   = cond action : matchBool action (pure t) cond
+unless = cond action : matchBool (pure t) action cond
+
+-- ---------------------------------------------------------------------------
+-- Infinite loop
+-- ---------------------------------------------------------------------------
+
+forever = y (self : action :
+  bind action (_ :
+    self action))
+
+-- ---------------------------------------------------------------------------
+-- Result-aware combinators
+-- ---------------------------------------------------------------------------
+
+-- Propagate driver Result on error; run okCase on success.
+onOk = action okCase :
+  bind action (result :
+    matchResult
+      (err rest : pure result)
+      okCase
+      result)
+
+-- Same as onOk, but the okCase only receives the value (rest is dropped).
+onOk_ = action okCase :
+  bind action (result :
+    matchResult
+      (err rest : pure result)
+      (val _ : okCase val)
+      result)
+
+-- Generalized Result handler with explicit branches.
+onResult = action errCase okCase :
+  bind action (result :
+    matchResult errCase okCase result)
+
+-- Same as onResult, but handlers only receive the value/msg (rest is dropped).
+onResult_ = action errCase okCase :
+  bind action (result :
+    matchResult
+      (err _ : errCase err)
+      (val _ : okCase val)
+      result)
 
 -- ---------------------------------------------------------------------------
 -- Convenience helpers
@@ -49,13 +98,9 @@ putStrLn = s : bind (putStr (append s "\n")) (_ : pure t)
 -- Result-aware file helpers
 -- ---------------------------------------------------------------------------
 
-onReadFile = (path errCase okCase :
-  bind (readFile path) (result :
-    matchResult errCase okCase result))
+onReadFile = path : onResult (readFile path)
 
-onWriteFile = (path contents errCase okCase :
-  bind (writeFile path contents) (result :
-    matchResult errCase okCase result))
+onWriteFile = path contents : onResult (writeFile path contents)
 
 -- ---------------------------------------------------------------------------
 -- Convenience helpers for the common cases
@@ -84,3 +129,18 @@ copyFile = (src dst :
                 (ok rest   : pure t)
                 wr))
         result))
+
+-- ---------------------------------------------------------------------------
+-- Resource-safe combinators
+-- ---------------------------------------------------------------------------
+
+finally = action cleanup :
+  bind action (result :
+    bind cleanup (_ :
+      pure result))
+
+bracket = acquire release use :
+  bind acquire (resource :
+    bind (use resource) (result :
+      bind (release resource) (_ :
+        pure result)))