Poly/ML 默认以 REPL 启动,类似于 SML/NJ。此外,您可以在运行时轻松调用编译器:它会为您生成本机代码,并以 LISP 中的方式将其添加到 ML 环境中eval
,但它是静态类型的真实机器代码,而不是解释代码。
该结构PolyML.Compiler
提供了各种(相对稳定的)接口来执行此操作,超出了官方 SML 标准。
这是 Poly/ML 5.5 或 5.6 的工作示例:
fun eval text =
let
fun print s = (TextIO.output (TextIO.stdOut, s); TextIO.flushOut TextIO.stdOut);
val line = ref 1;
val in_buffer = ref (String.explode text);
val out_buffer = ref ([]: string list);
fun output () = String.concat (rev (! out_buffer));
fun get () =
(case ! in_buffer of
[] => NONE
| c :: cs => (in_buffer := cs; if c = #"\n" then line := ! line + 1 else (); SOME c));
fun put s = out_buffer := s :: ! out_buffer;
fun put_message {message = msg1, hard, location = {startLine = line, ...}, context} =
(put (if hard then "Error: " else "Warning: ");
PolyML.prettyPrint (put, 76) msg1;
(case context of NONE => () | SOME msg2 => PolyML.prettyPrint (put, 76) msg2);
put ("Line " ^ Int.toString line ^ "\n"));
val parameters =
[PolyML.Compiler.CPOutStream put,
PolyML.Compiler.CPErrorMessageProc put_message,
PolyML.Compiler.CPLineNo (fn () => ! line)];
val _ =
(while not (List.null (! in_buffer)) do
PolyML.compiler (get, parameters) ())
handle exn =>
(put ("Exception- " ^ General.exnMessage exn ^ " raised");
print (output ()); raise exn);
in print (output ()) end;
现在我们可以像这样在普通的 Poly/ML REPL 中调用它:
> eval "1 + 1";
val it = 2: int
val it = (): unit
> eval "fun f 0 = 1 | f n = n * f (n - 1)";
val f = fn: int -> int
val it = (): unit
> eval "f 42";
val it = 1405006117752879898543142606244511569936384000000000: int
val it = (): unit
> f 42;
val it = 1405006117752879898543142606244511569936384000000000: int
这为您在 SML 的静态类型世界中提供了 LISP 风格的元编程。
请注意,结构PolyML.Compiler
有更多选项来控制运行时编译器调用的行为。最好在 polyml 邮件列表中询问它。