implement Terminal

nib/types/default.nix

@@ -2,10 +2,12 @@
   fault = import ./fault.nix args;
   maybe = import ./maybe.nix args;
   res = import ./res.nix args;
+  terminal = import ./terminal.nix args;
 in
   nib.std.mergeAttrsList [
     # submodule is included directly to this module (ie self.myFunc)
     fault
     maybe
     res
+    terminal
   ]

nib/types/terminal.nix

@@ -0,0 +1,21 @@
+{nib, ...}: rec {
+  # Terminal Monad
+  # Wrapper around a value (preserves lazy eval for the value)
+  Terminal = value: {
+    _nbtype_ = "nib::Terminal";
+    _value_ = value;
+  };
+
+  # Pattern Matching
+  isTerminal = T:
+    (builtins.attrNames T == ["_nbtype_" "_value_"])
+    && T._nbtype_ == "nib::Terminal";
+
+  # Unwrap (Monadic Return Operation)
+  unwrapTerminal = T:
+    assert isTerminal T || nib.panic.badType "Terminal" T;
+      T._value_;
+
+  # Map (Monadic Bind Operation)
+  mapTerminal = f: T: Terminal (f (unwrapTerminal T));
+}