refactor SML to be more portable

impls/sml/main.sml

@@ -1 +1 @@
-val _ = repl ()
+val _ = main ()

impls/sml/step0_repl.sml

@@ -21,3 +21,5 @@ fun repl () =
             )
             | NONE => ()
     ) end
+
+fun main () = repl ()

impls/sml/step1_read_print.sml

@@ -23,3 +23,5 @@ fun repl () =
             )
             | NONE => ()
     ) end
+
+fun main () = repl ()

impls/sml/step2_eval.sml

@@ -66,3 +66,5 @@ fun repl () =
             )
             | NONE => ()
     ) end
+
+fun main () = repl ()

impls/sml/step3_env.sml

@@ -62,9 +62,7 @@ val initEnv = ENV [] |> bind [
          | _     => raise NotApplicable "'/' requires arguments")
 ]
 
-fun repl () = repl' initEnv
-
-and repl' e =
+fun repl e =
     let open TextIO
     in (
         print("user> ");
@@ -73,7 +71,9 @@ and repl' e =
                 let val (e', s) = rep e line
                     val _ = print(s ^ "\n")
                 in
-                    repl' e'
+                    repl e'
                 end
             | NONE => ()
     ) end
+
+fun main () = repl initEnv

impls/sml/step4_if_fn_do.sml

@@ -51,9 +51,7 @@ fun rep e s =
 
 val initEnv = ENV [] |> bind coreNs
 
-fun repl () = repl' initEnv
-
-and repl' e =
+fun repl e =
     let open TextIO
     in (
         print("user> ");
@@ -62,7 +60,9 @@ and repl' e =
                 let val (e', s) = rep e line
                     val _ = print(s ^ "\n")
                 in
-                    repl' e'
+                    repl e'
                 end
             | NONE => ()
     ) end
+
+fun main () = repl initEnv