can you help me out, i made this program to get an output from some .txt file like this :
john:3:uk
paul:18:us
#load "str.cma"
let f_test = "/home/test.txt" ;;
(*
Recursive Reading function
*)
let read_lines f_test : string list =
if Sys.file_exists (f_test) then
begin
let ic = open_in f_test in
try
let try_read () =
try Some (input_line ic) with End_of_file -> None in
let rec loop acc = match try_read () with
| Some s -> loop (s :: acc)
| None -> close_in_noerr ic; List.rev acc in
loop []
with e ->
close_in_noerr ic;
[]
end
else
[]
;;
(*Using Records*)
type user =
{
name : string;
age : int;
country : string;
};;
(*
Function to separated info in list
*)
let rec splitinfo ?(sep=":") l = match l with
| [] -> []
| x::xs -> (Str.split (Str.regexp ":") x)::splitinfo xs;;
(*
Function to get users position
*)
let get_user l:user =
let age = int_of_string (List.nth l 1) in
let user_name = List.nth l 0 in
{
name = user_name;
age = age ;
country = List.nth l 2;
};;
(*
Function to check some parameter is valid
*)
let par1 u: int =
if (u.age = 3) then
1
else
0;;
(*
Reporting function
*)
let report_statistics list_users =
let child = ref 0 in
let teenager = ref 0 in
let adult = ref 0 in print_string (" ----- -- Stats -- ----- \n" ) ;
List.iter (
fun user_l -> (
match user_l with
| [] -> print_string("> no user <\n")
| _ ->
let user = get_user user_l in
if (par1 user = 1) then (
print_string (" "^ user.name ^" --> Child \n" ) ;
child := !child + 1;
)
else
print_string (" "^ user.name ^" --> Other \n" );
)
) list_users;
print_string ("------- List ---- ");
print_newline();
print_string ("Child " );
print_int(!child);
print_newline();
print_string ("Teenager ") ;
print_int(!teenager);
print_newline();
print_string ("Adult ");
print_int(!adult);
print_newline();
;;
The program compile but doesn't output any result ...
What am i missing ?
I kept the function to check parameters simple so i can understand it better but can't figure it out why it isn't outputing any result
Can you help me out here ?
Thanks in advance :)
The code as given defines some functions such as read_lines and report_statistics. But there are no calls to these functions.
If there is no other OCaml source involved, this is probably your problem. You need to call the functions.
It is fairly customary to have a "main" function that does the work of an OCaml program, and then (this is key) you have to actually call the main function:
let main () =
(* Call the functions that do the work of the program *)
let () = main ()
I have many times forgotten this last line and then nothing happens when I run the program.
Related
I'm implementing the Raft protocol and my code is as follows:
let rec request_vote_loop: int =
match myState.myRole with
| Follower -> 0
| Leader -> 1
| Candidate ->
let trigger = Domain.spawn(fun _ -> Chan.send c TriggerEvent) in
let request_vote_daemon = Domain.spawn(fun _ ->
let rec loop n =
if n = 0 then 0
else let msg = Chan.recv votes in
match msg with
| (status, id) ->
Domain.join (Array.get !arr id);
if status = 1 then (Array.get votePeers id) := true; (Chan.send c ReceiveVoteEvent); loop (n - 1)
in loop ((Array.length (!peers)) / 2 + 1 - !current_vote)) in
let evt = Chan.recv c in
match evt with
| TimeoutEvent -> myState.myRole <- Follower; 3
| AppendEntriesEvent(_) ->
myState.myRole <- Follower; 4
| ReceiveVoteEvent ->
if !current_vote > (Array.length (!peers) / 2) then
begin current_vote := !current_vote + 1; myState.myRole <- Leader; 3 end
else current_vote := !current_vote + 1; request_vote_loop
| TriggerEvent ->
arr := Array.make (Array.length (!peers)) (Domain.spawn (fun i ->
if (!(Array.get votePeers i)) then 0
else
let conn = Array.get !peers i in
Lwt_main.run
(let+ resp = call_server conn
(RequestVoteArg({
candidateNumber = myState.myPersistentState.id;
term = myState.myPersistentState.currentTerm;
lastlogIndex = (Array.get myState.myPersistentState.logs ((Array.length myState.myPersistentState.logs) - 1)).index;
lastlogTerm = (Array.get myState.myPersistentState.logs ((Array.length myState.myPersistentState.logs) - 1)).term
})) in (match resp with
| Error(s) -> Chan.send votes (0, i); Printf.printf "requestVote: connection failed: %s" s; 1
| Ok(repl, s) ->
(match repl with
| RequestVoteRet(repl) ->
if repl.voteGranted then begin Chan.send votes (1, i); Printf.printf "requestVote: status: %s, currentVote: %d" s !current_vote; 2 end
else
if not (repl.term = (-1l)) then begin myState.myPersistentState.currentTerm <- repl.term; Chan.send votes (0, i);
Printf.printf "requestVote failed because of term: status: %s, currentVote: %d" s !current_vote; 3 end
else Chan.send votes (0, i); Printf.printf "requestVote failed: status: %s" s; 4
| _ -> failwith "Should not reach here" ))))); request_vote_loop
| _ -> failwith "Should not reach here"
in print_endline (Int.to_string request_vote_loop)
But there's an error that "This kind of expression is not allowed as right-hand side of `let rec'", it said my function is of type unit. I don't know what happened...
Thanks in advance.
Your definition starts like this:
let rec request_vote_loop: int = ...
This doesn't define a function, it defines a simple value of type int. The reason is that there are no parameters given.
There's too much code to process (and furthermore it's not self-contained). But I suspect you want to define a function that doesn't take any parameters. The way to do this is to pass () (known as unit) as the parameter:
let rec request_vote_loop () : int = ...
The recursive calls look like this:
request_vote_loop ()
The final call looks like this:
Int.to_string (request_vote_loop ())
the code :
open Hashtbl;;
type 'a option = None | Some of 'a;;
let ht = create 0;;
let rec charCount fd =
let x =
try Some (input_char fd)
with End_of_file -> None
in
match x with
| Some c ->
let v =
try find ht c
with Not_found -> 0
in
replace ht c (v+1);
charCount fd
| None -> ();;
let loadHisto fn =
let fd = open_in fn in
charCount fd;;
let rec printList l = match l with
| [] -> print_newline ()
| h::t -> print_char h; print_string " "; printList t;;
let hashtbl_keys h = Hashtbl.fold (fun key _ l -> key :: l) h [];;
let compare_function a b = compare (find ht b) (find ht a);;
let akeys = List.sort compare_function (hashtbl_keys ht);;
printList (List.sort compare_function (hashtbl_keys ht));;
printList akeys;;
and the result :
ocaml histo.ml
e t s u a i n p j (*here is the first printList*)
(*and here should be the second one, but there is only a blank*)
Here is the problem :
I sorted a list, and tried to display it's content but as you can see, it doesn't seem like I can give a name to my resulting List
Edit :
I don't think it's a buffer problem because even if I only print akeys, there is nothing
Edit : I added the code asked for below
And ht is a hashtbl, and it contains what it should contain (I checked this)
I have a homework where i need to write 2 communication servers, one which generates natural numbers and the other which prints them. the generating server will be sending to the printing server. The servers should communicate over the shared channel chan.The main function should spawn a thread for each server.
`
val sender = fn : int -> unit
val receiver = fn : unit -> 'a
val main = fn : unit -> unit
`
And so far this is code i have written:
`
datatype 'a inflist = NIL
| CONS of 'a * (unit -> 'a inflist);
fun HD (CONS(a,b)) = a
| HD NIL = raise Subscript;
fun TL (CONS(a,b)) = b()
| TL NIL = raise Subscript;
fun NULL NIL = true
| NULL _ = false;
fun TAKE(xs, 0) = []
| TAKE(NIL, n) = raise Subscript
| TAKE(CONS(x,xf), n) = x::TAKE(xf(), n-1);
fun FROMN n = CONS (n,fn () => FROMN (n+1));
val natnumber = FROMN 0;
fun printGenList f (h::t) = (f h; printGenList f t);
fun printList l = printGenList (fn(e) => print(Int.toString(e)^" ")) l;
fun printPairList l = printGenList (fn(e,f) => print("("^Int.toString(e)^", "^Int.toString(f)^") ")) l;
CM.make "$cml/cml.cm";
open CML;
val chan: int chan = channel();
fun gen ch () = send (ch, printList(TAKE(natnumber,101)));
fun printnat ch () = recv (ch);
fun main () =
let
val ch = channel() :int chan ;
val _ = spawn (gen ch);
val _ = spawn (printnat ch);
in
()
end;
`
But i am not getting the output. Am i going wrong in my syntax or the logic?
I am new to SML and Concurrent ML. Please help me.
Why are you using a infinite list? There are simpler ways to implement this.
I'm trying to get a pretty print function to print the query result of my database in OCaml. I've been following this approach http://mancoosi.org/~abate/ocaml-format-module
I have this code so far:
let pp_cell fmt cell = Format.fprintf fmt "%s" cell;;
let pp_header widths fmt header =
let first_row = Array.map (fun x -> String.make (x + 1) ' ') widths in
Array.iteri (fun j cell ->
Format.pp_set_tab fmt ();
for z=0 to (String.length header.(j)) - 1 do cell.[z] <- header.(j).[z] done;
Format.fprintf fmt "%s" cell
) first_row
let pp_row pp_cell fmt row =
Array.iteri (fun j cell ->
Format.pp_print_tab fmt ();
Format.fprintf fmt "%a" pp_cell cell
) row
let pp_tables pp_row fmt (header,table) =
(* we build with the largest length of each column of the
* table and header *)
let widths = Array.create (Array.length table.(0)) 0 in
Array.iter (fun row ->
Array.iteri (fun j cell ->
widths.(j) <- max (String.length cell) widths.(j)
) row
) table;
Array.iteri (fun j cell ->
widths.(j) <- max (String.length cell) widths.(j)
) header;
(* open the table box *)
Format.pp_open_tbox fmt ();
(* print the header *)
Format.fprintf fmt "%a#\n" (pp_header widths) header;
(* print the table *)
Array.iter (pp_row fmt) table;
(* close the box *)
Format.pp_close_tbox fmt ();
;;
(** Pretty print answer set of a query in format of
* col_name 1 | col_name 2 | col_name 3 |
* result1.1 | result2.1 | result3.1 |
* result1.2 | result2.2 | result3.2 |
* #param col_names provides the names of columns in result outp ut *)
let pretty_print fmt pp_cell (col_names, tuples) =
match col_names with
| [] -> printf "Empty query\n"
| _ ->
printf "Tuples ok\n";
printf "%i tuples with %i fields\n" (List.length tuples) (List.length col_names);
print_endline(String.concat "\t|" col_names);
for i = 1 to List.length col_names do printf "--------" done; print_newline() ;
let print_row = List.iter (printf "%s\t|") in
List.iter (fun r -> print_row r ; print_newline ()) tuples;
for i = 1 to List.length col_names do printf "--------" done; print_newline() ;
let fmt = Format.std_formatter in
Format.fprintf fmt "%a" (pp_tables (pp_row pp_cell)) (Array.of_list col_names,tuples);
flush stdout
;;
let print_res (col_names, tuples) =
let fmt = Format.std_formatter in
pretty_print fmt pp_cell (col_names, tuples)
;;
The problem is in the line
Format.fprintf fmt "%a" (pp_tables (pp_row pp_cell)) (Array.of_list col_names,tuples);
basically because I need tuples to be and string array array (a matrix) while its type is string list list. So I tried to solve it by converting the list list into a matrix following this approach http://www.siteduzero.com/forum-83-589601-p1-ocaml-convertir-un-list-list-en-array-array.html with this code:
let listToMatrix lli =
let result = Array.init 6 (fun _ -> Array.create 7 2)
let rec outer = function
| h :: tl, col ->
let rec inner = function
| h :: tl, row ->
result.[row].[col] <- h
inner (tl, row + 1)
| _ -> ()
inner (h, 6 - List.length h)
outer (tl, col + 1)
| _ -> ()
outer (lli, 0)
result
;;
But I just a syntax error while compiling:
File "src/conn_ops.ml", line 137, characters 2-5:
Error: Syntax error
make: *** [bin/conn_ops.cmo] Error 2
I don't really know what to do, or how I can accomplish the conversation of the list list into the matrix. My approach is the correct? This has been the first time I've worked with OCaml and it's been quite a pain in the *, so please, try to be kind with me :D
This is a lot of code to read in detail, but it looks like you're missing a semicolon after result.[row].[col] <- h. However, this code looks suspicious to me. The notation .[xxx] is for accessing individual characters of a string. You want to use array index notation .(xxx), seems to me.
Here is a function that changes a string list list to a string array array. Maybe it will be useful:
let sll_to_saa sll = Array.of_list (List.map Array.of_list sll)
Actually, this function changes any list of lists to an array of arrays; it doesn't have to be strings.
I'm not sure I understood your entire post, but if you want to convert
a string list list into a string array array, you can do this
quite easily with the Array.of_list function:
# let strings = [["hello"; "world"]; ["foo"; "bar"]];;
val strings : string list list = [["hello"; "world"]; ["foo"; "bar"]]
# Array.of_list (List.map Array.of_list strings);;
- : string array array = [|[|"hello"; "world"|]; [|"foo"; "bar"|]|]
I hope this helped.
Your function is not syntacticly correct. Below is a fixed version:
let listToMatrix lli =
let result = Array.init 6 (fun _ -> Array.create 7 2) in
let rec outer = function
| h :: tl, col ->
let rec inner = function
| h :: tl, row ->
result.(row).(col) <- h;
inner (tl, row + 1)
| _ -> ()
in
inner (h, 6 - List.length h);
outer (tl, col + 1)
| _ -> ()
in
outer (lli, 0);
result
;;
As noted in other answers:
the subscript operators for arrays are parentheses,
some semi-colons are missing,
sometimes you forget to use the keyword in to mark the expression where your definition will be used.
Please note that I didn't check if the function does what it is supposed to do.
I want to do something as simple as this:
Print a list.
let a = [1;2;3;4;5]
How can I print this list to Standard Output?
You should become familiar with the List.iter and List.map functions. They are essential for programming in OCaml. If you also get comfortable with the Printf module, you can then write:
open Printf
let a = [1;2;3;4;5]
let () = List.iter (printf "%d ") a
I open Printf in most of my code because I use the functions in it so often. Without that you would have to write Printf.printf in the last line. Also, if you're working in the toploop, don't forget to end the above statements with double semi-colons.
You can do this with a simple recursion :
let rec print_list = function
[] -> ()
| e::l -> print_int e ; print_string " " ; print_list l
The head of the list is printed, then you do a recursive call on the tail of the list.
print_string (String.concat " " (List.map string_of_int list))
If the question is about finding the quickiest way to implement this, for example when debugging, then we could say that:
extended standard libraries (e.g. batteries) typically have some additional functions:
List.print
~first:"[" ~sep:";" ~last:"]" (fun c x -> Printf.fprintf c "%d" x) stdout a
this tiny syntax extension that I wrote some time ago allows you to write:
<:print<[$!i <- a${$d:i$}{;}]>>
automatic generation is not immediately available (because of the lack of run-time type information in OCaml data representation) but can be achieved using either code generation from the types, or run-time types.
I'm very late answering, but here's another way:
let print_list f lst =
let rec print_elements = function
| [] -> ()
| h::t -> f h; print_string ";"; print_elements t
in
print_string "[";
print_elements lst;
print_string "]";;
To print an int list, we could write:
print_list print_int [3;6;78;5;2;34;7];;
However if we were going to do this a lot, it would save time to specialize the function using partial application:
let print_int_list = print_list print_int;;
Which we can now use like so:
print_int_list [3;6;78;5;2;34;7];;
What if we wanted to do something pretty complex, like printing an int list list? With this function, it's easy:
(* Option 1 *)
print_list (print_list print_int) [[3;6;78];[];[5];[2;34;7]];;
(* Option 2 *)
let print_int_list_list = print_list (print_list print_int);;
print_int_list_list [[3;6;78];[];[5];[2;34;7]];;
(* Option 3 *)
let print_int_list_list = print_list print_int_list;;
print_int_list_list [[3;6;78];[];[5];[2;34;7]];;
Printing an (int * string) list (i.e. a list of pairs of ints and strings):
(* Option 1 *)
print_list (fun (a, b) -> print_string "("; print_int a; print_string ", "; print_string b; print_string ")") [(1, "one"); (2, "two"); (3, "three")];;
(* Option 2 *)
let print_pair f g (a, b) =
print_string "(";
f a;
print_string ", ";
g b;
print_string ")";;
print_list (print_pair print_int print_string) [(1, "one"); (2, "two"); (3, "three")];;
(* Option 3 *)
let print_pair f g (a, b) =
print_string "(";
f a;
print_string ", ";
g b;
print_string ")";;
let print_int_string_pair = print_pair print_int print_string;;
print_list print_int_string_pair [(1, "one"); (2, "two"); (3, "three")];;
(* Option 4 *)
let print_pair f g (a, b) =
print_string "(";
f a;
print_string ", ";
g b;
print_string ")";;
let print_int_string_pair = print_pair print_int print_string;;
let print_int_string_pair_list = print_list print_int_string_pair;;
print_int_string_pair_list [(1, "one"); (2, "two"); (3, "three")];;
I would do this in the following way:
let a = [1;2;3;4;5];;
List.iter print_int a;;
Actually, you can decouple printing a list and turning a list into a string. The main advantage for doing this is that you can use this method to show lists in logs, export them to CSVs...
I often use a listHelper module, with the following :
(** Generic method to print the elements of a list *)
let string_of_list input_list string_of_element sep =
let add a b = a^sep^(string_of_element b) in
match input_list with
| [] -> ""
| h::t -> List.fold_left add (string_of_element h) t
So, if I wanted to output a list of floats to a csv file, I could just use the following :
let float_list_to_csv_row input_list = string_of_list input_list string_of_float ","
Just a solution with %a :
open Printf
let print_l outx l =
List.map string_of_int l
|> String.concat ";"
|> fprintf outx "%s"
Test :
# printf "[%a]" print_l [1;2;3] ;;
[1;2;3]- : unit = ()
# printf "[%a]" print_l [];;
[]- : unit = ()
let print_list l =
let rec aux acc =
match acc with
| [] -> ()
| x :: tl ->
Printf.fprintf stdout "%i"; aux tl
in aux l
Or
let sprintf_list l =
let acc = ref "{" in
List.iteri (fun i x ->
acc := !acc ^
if i <> 0
then Printf.sprintf "; %i" x
else Printf.sprintf "%i" x
) l;
!acc ^ "}"
let print_list l =
let output = sprintf_list l in
Printf.fprintf stdout "%s\n" output