remove main from Tour.newt since it is no longer required

playground/samples/Tour.newt

@@ -95,8 +95,9 @@ foo : Nat -> Nat -> Nat
 foo a b = ?
 
 -- Newt compiles to javascript, there is a tab to the right that shows the
--- javascript output. It is not doing erasure (or inlining) yet, so the
--- code is a little verbose.
+-- javascript output. There is some erasure, but inlining is not being done
+-- yet.  Dead code elimination will be done if there is a `main` function.
+-- That is not the case in this file.
 
 -- We can define native types, if the type is left off, it defaults to U
 
@@ -210,32 +211,3 @@ prod xs ys = do
   y <- ys
   pure (x, y)
 
--- The playground is compiling to javascript and will give an error if
--- main isn't implemented, so I'll crib the definition of IO from
--- Prelude:
-
-data Unit : U where
-  MkUnit : Unit
-
-ptype World
-
-data IORes : U -> U where
-  MkIORes : ∀ a. a -> World -> IORes a
-
-IO : U -> U
-IO a = World -> IORes a
-
-instance Monad IO where
-  bind ma mab = \ w => case ma w of
-    MkIORes a w => mab a w
-  pure a = \ w => MkIORes a w
-
--- Here we declare `uses` to let the dead code elimination know we're poking
--- at MKIORes and MkUnit behind the compiler's back.
-pfunc putStrLn uses (MkIORes MkUnit) : String -> IO Unit := `(s) => (w) => {
-  console.log(s)
-  return MkIORes(undefined,MkUnit,w)
-}`
-
-main : IO Unit
-main = putStrLn "hello, world"