ocaml

问题 I'm studying on how to integrate an OCaml TCP/IP stack into my C++ project. I already know how to call C from OCaml and call OCaml from C thanks to this answer: OCaml as C library, hello world example The OCaml will be controlled by C++, not the other way around. So, for a TCP/IP stack, I must be able to send and receive packets. I can easily send data to the TCP/IP stack through C++, but how to receive it? I need to pass a C function (a callback) as a parameter to OCaml so it delivers the

问题 According to this answer, F# supports OCaml style type parameters. The example in the question is: type 'a NestedList = List of 'a NestedList list | Elem of 'a However, I could not find this syntax documented anywhere in the F# documentation and moreover, I cannot get the F# compiler accept the syntax in the answer I gave the link to. This attempt to use multiple parameters are not accepted by the compiler: type ('a * 'b) SomeType = ('a * 'b) This however, works: type ('a , 'b) SomeType = ('a

问题 Currently I have some code in this way: method printFuncIntoFile X = let funHead = "head" and funbody = "body" and oc = open_out "test.txt" in Printf.fprintf oc "%s%s" funHead funBody; close_out oc; foo X.child And this code can only leave the last function content in the text.txt. I search the Printf document but can only find a val bprintf : Buffer.t -> ('a, Buffer.t, unit) format -> 'a which requires a Buffer data structure, I think there should be some strategies more easy, even though I

问题 Currently I have some code in this way: method printFuncIntoFile X = let funHead = "head" and funbody = "body" and oc = open_out "test.txt" in Printf.fprintf oc "%s%s" funHead funBody; close_out oc; foo X.child And this code can only leave the last function content in the text.txt. I search the Printf document but can only find a val bprintf : Buffer.t -> ('a, Buffer.t, unit) format -> 'a which requires a Buffer data structure, I think there should be some strategies more easy, even though I

问题 Currently I have some code in this way: method printFuncIntoFile X = let funHead = "head" and funbody = "body" and oc = open_out "test.txt" in Printf.fprintf oc "%s%s" funHead funBody; close_out oc; foo X.child And this code can only leave the last function content in the text.txt. I search the Printf document but can only find a val bprintf : Buffer.t -> ('a, Buffer.t, unit) format -> 'a which requires a Buffer data structure, I think there should be some strategies more easy, even though I

问题 Currently I have some code in this way: method printFuncIntoFile X = let funHead = "head" and funbody = "body" and oc = open_out "test.txt" in Printf.fprintf oc "%s%s" funHead funBody; close_out oc; foo X.child And this code can only leave the last function content in the text.txt. I search the Printf document but can only find a val bprintf : Buffer.t -> ('a, Buffer.t, unit) format -> 'a which requires a Buffer data structure, I think there should be some strategies more easy, even though I

问题 Suppose type pair_int = {l1:int; l2:int, ..., ln:int} let test = {l1=2; l2=4, ..., ln=71} I thought I could do something like map (fun (x,y) -> y) test , but it doesn't work How can I get the list [2,4, ..., 71] from test ? 回答1: There's no nice way to do this inside the OCaml type system. You can't map over the fields of a record because they can be of all different types. Your type pair_int looks suspiciously like a list or an array already. The field names don't add any semantic content,

问题 I can use the following function to overwrite a text file: let writeFile ~filename:fn s = let oc = open_out fn in output_string oc s; close_out oc ;; Howeve, i donot know how to append a line to a text file ? 回答1: You could pass additional mode flag Open_append to open_out_gen function: let _ = let oc = open_out_gen [Open_creat; Open_text; Open_append] 0o640 "a.txt" in output_string oc "append\n"; close_out oc 回答2: This is what I do: let append_string path s = let chan = open_out_gen [Open

问题 I'm trying to use the technique in Composable Error Handling in OCaml (Result type with polymorphic variants for errors) for some code I've written. The types of the functions I'm trying to use look like this: val parse : parser -> token list -> (Nominal.term, [> `ParseError of string ]) Result.t val lex : lexer -> string -> (token list, [> `LexError of string ]) Result.t My attempt at composing them is this: let lex_and_parse : parser -> lexer -> string -> (Nominal.term, [> `ParseError of

问题 (This is an extension / distillation of Polymorphic variants and let%bind type error) Consider the following code: Version 1: let x : [> `Error1 ] = (`Error1 : [> `Error1 ]) let y : [> `Error1 | `Error2 ] = x Version 2: let x : [> `Error1 ] = (`Error1 : [ `Error1 ]) let y : [> `Error1 | `Error2 ] = x Version 1 typechecks, but version 2 fails (I'm compiling with 4.09.0): File "test.ml", line 2, characters 33-34: 2 | let y : [> `Error1 | `Error2 ] = x ^ Error: This expression has type [ `Error1