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+---
+title: .NET AOT 下的 F# 命令行参数解析库选择
+date: 2024-06-06 20:50:35
+tags: [Technique]
+---
+
+Argu 不支持 AOT，不过用 F# 的话可以看整个 .NET 的生态，我看了一下 C# 的 CommandLineParser：
+https://github.com/commandlineparser
+
+在这个 PR 中支持了 Native AOT
+https://github.com/commandlineparser/commandline/pull/913
+
+除此之外，还有一个更加精巧的 F# 库可以用，只有两百多行：
+https://github.com/B2R2-org/FsOptParse/
+
+AOT 后的大小很可观，并且支持 full trim.
+
+用例：
+
+```fsharp
+(** defines a state to pass to the option parser *)
+type opts =
+  {
+    optX : int;
+    optY : bool;
+    optZ : string;
+  }
+
+(** default option state *)
+let defaultOpts =
+  {
+    optX = 0;
+    optY = false;
+    optZ = "";
+  }
+
+(*
+  An example command line specification, which is a list of Options.
+  Each Option describes a command line option (switch) that is specified with
+  either a short (a single-dash option) or long option (a double-dash option).
+*)
+let spec =
+  [
+    (* This option can be specified with -x <NUM>. There is an extra argument to
+       specify a value in integer. *)
+    Option ((* description of the option *)
+            descr="this is a testing param X",
+            (* how many extra argument must be provided by a user? *)
+            extra=1,
+            (* callback sets up the option and returns it *)
+            callback=(fun opts arg -> {opts with optX=(int) arg.[0]}),
+            (* use a short option style -x *)
+            short="-x"
+           );
+
+    (* This option can be specified with -y. There is no extra argument. This
+       option just sets a flag, optY. *)
+    Option ((* description of the option *)
+            descr="this is a testing param Y",
+            (* set the option to be true *)
+            callback=(fun opts _ -> {opts with optY=true}),
+            (* use a short option style (-y) *)
+            short="-y",
+            (* also use a long option style (--yoohoo) *)
+            long="--yoohoo"
+           );
+
+    (* A dummy option to pretty-print the usage *)
+    Option ((* description of the option *)
+            descr="",
+            dummy=true
+           );
+    Option ((* description of the option *)
+            descr="[Required Options]",
+            descrColor=System.ConsoleColor.DarkCyan,
+            dummy=true
+           );
+
+    (* The third option is a required option. In other words, option parsing
+       will raise an exception if this option is not given by a user. This
+       option takes in an additional integer argument, and set it to the global
+       variable z. *)
+    Option ((* description of the option *)
+            descr="required parameter <STRING> with an integer option",
+            (* callback to set the optZ value *)
+            callback=(fun opts arg -> {opts with optZ=arg.[0]}),
+            (* specifying this is a required option *)
+            required=true,
+            (* one additional argument to specify an integer value *)
+            extra=1,
+            (* use only a long option style *)
+            long="--req"
+           );
+  ]
+
+let _ =
+  let prog = "opttest.fsx"
+  let args = System.Environment.GetCommandLineArgs ()
+  let usageGetter () = "[Usage]\n  %p %o"
+  try
+    let left, opts = optParse spec usageGetter prog args defaultOpts
+    printfn "Rest args: %A, x: %d, y: %b, z: %s"
+      left opts.optX opts.optY opts.optZ
+    0
+  with
+    | SpecErr msg ->
+        eprintfn "Invalid spec: %s" msg
+        exit 1
+    | RuntimeErr msg ->
+        eprintfn "Invalid args given by user: %s" msg
+        usagePrint spec prog usageGetter (fun () -> exit 1)
+```