Code snippet works in an online IDE but not on my local ghc - ghc
As a beginner, i wrote a snippet to flip a string's case.
module Main
where
import Data.Char
main=do
str<-getLine
putStrLn ( reverser(str) )
reverser:: String -> String
reverser [] = []
reverser (x:xs) | isUpper x = toLower x : reverser xs
| otherwise = toUpper x : reverser xs
And it worked perfectly on the hackerearth.com's IDE
IDE screenshot
However,when I tried running the same on my machine, the code is executing endlessly and not coming up with any output nor error.
Terminal
What am I doing wrong?
Related
OCaml - Error: Module `Unix' is unavailable [closed]
Closed. This question needs debugging details. It is not currently accepting answers. Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question. Closed last year. Improve this question I have been working through Harvard's CS51 class using materials available online. I'm trying to start the final project and downloaded the necessary files, but when I try to compile them I get the following error: Error: Module `Unix' is unavailable (required by `Thread') Command exited with code 2. Compilation unsuccessful after building 18 targets (15 cached) in 00:00:00. I have not made any changes to the code I downloaded yet and supposedly I should be able to compile it successfully in its current state. Any ideas why I might be getting this error? EDIT: Below is the code from the file I downloaded and am trying to compile. module Ev = Evaluation ;; module MP = Miniml_parse ;; module ML = Miniml_lex ;; module Ex = Expr ;; open Printf ;; (* str_to_exp str -- Returns the expression specified by `str` using the MiniML parser. *) let str_to_exp (str: string) : Ex.expr = let lexbuf = Lexing.from_string str in let exp = MP.input ML.token lexbuf in exp ;; (* repl () -- Read-eval-print loop for MiniML, which prompts for and evaluates MiniML expressions, printing the resulting value. Exits the loop and terminates upon reading an end-of-file (control-d). *) let repl () = (* lexical analyzer buffer from stdin *) let lexbuf = Lexing.from_channel stdin in (* set up the initial environment *) let env = Ev.Env.empty () in (* the main LOOP *) while true do (try (* prompt *) printf "<== %!"; (* READ and parse an expression from the input *) let exp = MP.input ML.token lexbuf in (* EVALuate it *) let res = Ev.evaluate exp env in (* PRINT the result; in this initial version, the trivial evaluator just returns the expression unchanged as an element of the `Env.value` type (found in `expr.ml`), so we just extract the expression back out and print it *) match res with | Val resexp -> printf "==> %s\n" (Ex.exp_to_abstract_string resexp) | _ -> failwith "not handling other cases yet" with | MP.Error -> printf "xx> parse error\n" | Ev.EvalError msg -> printf "xx> evaluation error: %s\n" msg | Ev.EvalException -> printf "xx> evaluation exception\n" | End_of_file -> printf "Goodbye.\n"; exit 0 ); flush stdout done ;; (* Run REPL if called from command line *) try let _ = Str.search_forward (Str.regexp "miniml\\.\\(byte\\|native\\|bc\\|exe\\)") (Sys.argv.(0)) 0 in repl () with Not_found -> () ;; If I add open Unix it does take care of the error above, but I then get a different error: 26 | let lexbuf = Lexing.from_channel stdin in ^^^^^ Error: This expression has type Unix.file_descr but an expression was expected of type in_channel Command exited with code 2.
Generally, you have to explicitly ask to be linked to the Unix module. The following program: $ cat main.ml Unix.gethostname () |> print_endline would need to be built like this: $ ocamlfind opt -linkpkg -package unix -o main main.ml; echo $? 0 whereas the bare minimum would fail with a similar error as yours: $ ocamlopt -o main main.ml; echo $? File "main.ml", line 1: Error: No implementations provided for the following modules: Unix referenced from main.cmx 2 That said, it looks like you're using Core, in which case (as well as most other cases, actually) you're probably better off with dune: $ cat dune (executable (name main) (libraries unix)) $ dune build main.exe $ ./_build/default/main.exe amam-oy However, if you ask Dune to link you to Core, Unix is already included automatically, so the following dune file would also work for the above program: $ cat dune (executable (name main) (libraries core))
Just add open Unix;; at the very start of your .ml file
Syntactical issue between order of two functions
Is there any order to be maintained while placing functions one another? I just tried the code on the online compiler provided by purescript.org itself "http://try.purescript.org" module Main where import Prelude import Data.List import Data.Array ((..)) import Data.Traversable (traverse) import Control.Monad.Eff.Console(log) import TryPureScript(render,withConsole) main = render =<< withConsole do log $ "Hello world" traverse (\x -> log $ show $ x) (1..10) log $ "Hello world" The code is compiling absolutely fine when the last log function is removed or when the traverse function is removed.But its not working while they are placed in such an order.These two(log & traverse) functions are working perfectly individually but not together.Help me to get out of this issue.
I think the error message already give you a hint, you can fix by _ <- traverse (\x -> log $ show $ x) (1..10) -- or void $ traverse (\x -> log $ show $ x) (1..10)
Ejabberd: error in simple module to handle offline messages
I have an Ejabberd 17.01 installation where I need to push a notification in case a recipient is offline. This seems the be a common task and solutions using a customized Ejabberd module can be found everywhere. However, I just don't get it running. First, here's me script:
-module(mod_offline_push).
-behaviour(gen_mod).
-export([start/2, stop/1]).
-export([push_message/3]).
-include("ejabberd.hrl").
-include("logger.hrl").
-include("jlib.hrl").
start(Host, _Opts) ->
?INFO_MSG("mod_offline_push loading", []),
ejabberd_hooks:add(offline_message_hook, Host, ?MODULE, push_message, 10),
ok.
stop(Host) ->
?INFO_MSG("mod_offline_push stopping", []),
ejabberd_hooks:add(offline_message_hook, Host, ?MODULE, push_message, 10),
ok.
push_message(From, To, Packet) ->
?INFO_MSG("mod_offline_push -> push_message", [To]),
Type = fxml:get_tag_attr_s(<<"type">>, Packet), % Supposedly since 16.04
%Type = xml:get_tag_attr_s(<<"type">>, Packet), % Supposedly since 13.XX
%Type = xml:get_tag_attr_s("type", Packet),
%Type = xml:get_tag_attr_s(list_to_binary("type"), Packet),
?INFO_MSG("mod_offline_push -> push_message", []),
ok.
The problem is the line Type = ... line in method push_message; without that line the last info message is logged (so the hook definitely works). When browsing online, I can find all kinds of function calls to extract elements from Packet. As far as I understand it changed over time with new releases. But it's not good, all variants lead in some kind of error. The current way returns:
2017-01-25 20:38:08.701 [error] <0.21678.0>#ejabberd_hooks:run1:332 {function_clause,[{fxml,get_tag_attr_s,[<<"type">>,{message,<<>>,normal,<<>>,{jid,<<"homer">>,<<"xxx.xxx.xxx.xxx">>,<<"conference">>,<<"homer">>,<<"xxx.xxx.xxx.xxx">>,<<"conference">>},{jid,<<"carl">>,<<"xxx.xxx.xxx.xxx">>,<<>>,<<"carl">>,<<"xxx.xxx.xxx.xxx">>,<<>>},[],[{text,<<>>,<<"sfsdfsdf">>}],undefined,[],#{}}],[{file,"src/fxml.erl"},{line,169}]},{mod_offline_push,push_message,3,[{file,"mod_offline_push.erl"},{line,33}]},{ejabberd_hooks,safe_apply,3,[{file,"src/ejabberd_hooks.erl"},{line,382}]},{ejabberd_hooks,run1,3,[{file,"src/ejabberd_hooks.erl"},{line,329}]},{ejabberd_sm,route,3,[{file,"src/ejabberd_sm.erl"},{line,126}]},{ejabberd_local,route,3,[{file,"src/ejabberd_local.erl"},{line,110}]},{ejabberd_router,route,3,[{file,"src/ejabberd_router.erl"},{line,87}]},{ejabberd_c2s,check_privacy_route,5,[{file,"src/ejabberd_c2s.erl"},{line,1886}]}]}
running hook: {offline_message_hook,[{jid,<<"homer">>,<<"xxx.xxx.xxx.xxx">>,<<"conference">>,<<"homer">>,<<"xxx.xxx.xxx.xxx">>,<<"conference">>},{jid,<<"carl">>,<<"xxx.xxx.xxx.xxx">>,<<>>,<<"carl">>,<<"xxx.xxx.xxx.xxx">>,<<>>},{message,<<>>,normal,<<>>,{jid,<<"homer">>,<<"xxx.xxx.xxx.xxx">>,<<"conference">>,<<"homer">>,<<"xxx.xxx.xxx.xxx">>,<<"conference">>},{jid,<<"carl">>,<<"xxx.xxx.xxx.xxx">>,<<>>,<<"carl">>,<<"xxx.xxx.xxx.xxx">>,<<>>},[],[{text,<<>>,<<"sfsdfsdf">>}],undefined,[],#{}}]}
I'm new Ejabberd and Erlang, so I cannot really interpret the error, but the Line 33 as mentioned in {mod_offline_push,push_message,3,[{file,"mod_offline_push.erl"}, {line,33}]} is definitely the line calling get_tag_attr_s.
UPDATE 2017/01/27: Since this cost me a lot of headache -- and I'm still not perfectly happy -- I post here my current working module in the hopes it might help others. My setup is Ejabberd 17.01 running on Ubuntu 16.04. Most stuff I tried and failed with seem to for older versions of Ejabberd:
-module(mod_fcm_fork).
-behaviour(gen_mod).
%% public methods for this module
-export([start/2, stop/1]).
-export([push_notification/3]).
%% included for writing to ejabberd log file
-include("ejabberd.hrl").
-include("logger.hrl").
-include("xmpp_codec.hrl").
%% Copied this record definition from jlib.hrl
%% Including "xmpp_codec.hrl" and "jlib.hrl" resulted in errors ("XYZ already defined")
-record(jid, {user = <<"">> :: binary(),
server = <<"">> :: binary(),
resource = <<"">> :: binary(),
luser = <<"">> :: binary(),
lserver = <<"">> :: binary(),
lresource = <<"">> :: binary()}).
start(Host, _Opts) ->
?INFO_MSG("mod_fcm_fork loading", []),
% Providing the most basic API to the clients and servers that are part of the Inets application
inets:start(),
% Add hook to handle message to user who are offline
ejabberd_hooks:add(offline_message_hook, Host, ?MODULE, push_notification, 10),
ok.
stop(Host) ->
?INFO_MSG("mod_fcm_fork stopping", []),
ejabberd_hooks:add(offline_message_hook, Host, ?MODULE, push_notification, 10),
ok.
push_notification(From, To, Packet) ->
% Generate JID of sender and receiver
FromJid = lists:concat([binary_to_list(From#jid.user), "#", binary_to_list(From#jid.server), "/", binary_to_list(From#jid.resource)]),
ToJid = lists:concat([binary_to_list(To#jid.user), "#", binary_to_list(To#jid.server), "/", binary_to_list(To#jid.resource)]),
% Get message body
MessageBody = Packet#message.body,
% Check of MessageBody is not empty
case MessageBody/=[] of
true ->
% Get first element (no idea when this list can have more elements)
[First | _ ] = MessageBody,
% Get message data and convert to string
MessageBodyText = binary_to_list(First#text.data),
send_post_request(FromJid, ToJid, MessageBodyText);
false ->
?INFO_MSG("mod_fcm_fork -> push_notification: MessageBody is empty",[])
end,
ok.
send_post_request(FromJid, ToJid, MessageBodyText) ->
%?INFO_MSG("mod_fcm_fork -> send_post_request -> MessageBodyText = ~p", [Demo]),
Method = post,
PostURL = gen_mod:get_module_opt(global, ?MODULE, post_url,fun(X) -> X end, all),
% Add data as query string. Not nice, query body would be preferable
% Problem: message body itself can be in a JSON string, and I couldn't figure out the correct encoding.
URL = lists:concat([binary_to_list(PostURL), "?", "fromjid=", FromJid,"&tojid=", ToJid,"&body=", edoc_lib:escape_uri(MessageBodyText)]),
Header = [],
ContentType = "application/json",
Body = [],
?INFO_MSG("mod_fcm_fork -> send_post_request -> URL = ~p", [URL]),
% ADD SSL CONFIG BELOW!
%HTTPOptions = [{ssl,[{versions, ['tlsv1.2']}]}],
HTTPOptions = [],
Options = [],
httpc:request(Method, {URL, Header, ContentType, Body}, HTTPOptions, Options),
ok.
Actually it fails with second arg Packet you pass to fxml:get_tag_attr_s in push_message function
{message,<<>>,normal,<<>>,
{jid,<<"homer">>,<<"xxx.xxx.xxx.xxx">>,<<"conference">>,
<<"homer">>,<<"xxx.xxx.xxx.xxx">>,<<"conference">>},
{jid,<<"carl">>,<<"xxx.xxx.xxx.xxx">>,<<>>,<<"carl">>,
<<"xxx.xxx.xxx.xxx">>,<<>>},
[],
[{text,<<>>,<<"sfsdfsdf">>}],
undefined,[],#{}}
because it is not xmlel
Looks like it is record "message" defined in tools/xmpp_codec.hrl
with <<>> id and type 'normal'
xmpp_codec.hrl
-record(message, {id :: binary(),
type = normal :: 'chat' | 'error' | 'groupchat' | 'headline' | 'normal',
lang :: binary(),
from :: any(),
to :: any(),
subject = [] :: [#text{}],
body = [] :: [#text{}],
thread :: binary(),
error :: #error{},
sub_els = [] :: [any()]}).
Include this file and use just
Type = Packet#message.type
or, if you expect binary value
Type = erlang:atom_to_binary(Packet#message.type, utf8)
The newest way to do that seems to be with xmpp:get_type/1: Type = xmpp:get_type(Packet), It returns an atom, in this case normal.
Error attempting to decode with wreq
I'm trying really hard to understand how to use lenses and wreq and its turning out to really slow me down.
The error seems to be claiming there's some mismatched type here. I'm not sure exactly how to handle that though. I'm still fairly new to haskell and these lenses are pretty confusing. However, wreq seems to be cleaner, which is why I chose to use it. Can anyone help me understand what the error is, and how to fix it? I seem to run into alot of these type errors. I am aware that Maybe TestInfo won't be returned by my code at the moment. That's ok. That error know how to handle. This error however, I don't.
Here is my code:
Module TestInformation:
{-# LANGUAGE OverloadedStrings #-}
module TestInformation where
import Auth
import Network.Wreq
import Control.Lens
import Data.Aeson
import Data.Aeson.Lens (_String)
type TestNumber = String
data TestInfo = TestInfo {
TestId :: Int,
TestName :: String,
}
instance FromJSON TestInfo
getTestInfo :: Key -> TestNumber -> Maybe TestInfo
getTestInfo key test =
decode (res ^. responseBody . _String)
where opts = defaults & auth ?~ oauth2Bearer key
res = getWith opts ("http://testsite.com/v1/tests/" ++ test)
Module Auth:
module Auth where
import qualified Data.ByteString as B
type Key = B.ByteString
The error:
GHCi, version 7.10.1: http://www.haskell.org/ghc/ :? for help
[1 of 2] Compiling Auth ( Auth.hs, interpreted )
[2 of 2] Compiling TestInformation ( TestInformation.hs, interpreted )
TestInformation.hs:36:18:
Couldn't match type ‘Response body10’
with ‘IO (Response Data.ByteString.Lazy.Internal.ByteString)’
Expected type: (body10
-> Const Data.ByteString.Lazy.Internal.ByteString body10)
-> IO (Response Data.ByteString.Lazy.Internal.ByteString)
-> Const
Data.ByteString.Lazy.Internal.ByteString
(IO (Response Data.ByteString.Lazy.Internal.ByteString))
Actual type: (body10
-> Const Data.ByteString.Lazy.Internal.ByteString body10)
-> Response body10
-> Const Data.ByteString.Lazy.Internal.ByteString (Response body10)
In the first argument of ‘(.)’, namely ‘responseBody’
In the second argument of ‘(^.)’, namely ‘responseBody . _String’
TestInformation.hs:36:33:
Couldn't match type ‘Data.ByteString.Lazy.Internal.ByteString’
with ‘Data.Text.Internal.Text’
Expected type: (Data.ByteString.Lazy.Internal.ByteString
-> Const
Data.ByteString.Lazy.Internal.ByteString
Data.ByteString.Lazy.Internal.ByteString)
-> body10 -> Const Data.ByteString.Lazy.Internal.ByteString body10
Actual type: (Data.Text.Internal.Text
-> Const
Data.ByteString.Lazy.Internal.ByteString Data.Text.Internal.Text)
-> body10 -> Const Data.ByteString.Lazy.Internal.ByteString body10
In the second argument of ‘(.)’, namely ‘_String’
In the second argument of ‘(^.)’, namely ‘responseBody . _String’
Failed, modules loaded: Auth.
Leaving GHCi.
This type checks for me:
getTestInfo :: Key -> TestNumber -> IO (Maybe TestInfo)
getTestInfo key test = do
res <- getWith opts ("http://testsite.com/v1/tests/" ++ test)
return $ decode (res ^. responseBody)
where opts = defaults & auth ?~ oauth2Bearer key
getWith is an IO action, so to get its return value you need to use the monadic binding operator <-.
Full program: http://lpaste.net/133443 http://lpaste.net/133498
Download pdf file from wikipedia
Wikipedia provides a link (left side on Print/export) on every article to download the article as pdf. I wrote a small Haskell script which first gets the Wikipedia link and output the rendering link. When I am giving the rendering url as input, I am getting empty tags but the same url in browser provides download link. Could someone please tell me how to solve this problem? Formated code on ideone. import Network.HTTP import Text.HTML.TagSoup import Data.Maybe parseHelp :: Tag String -> Maybe String parseHelp ( TagOpen _ y ) = if any ( \( a , b ) -> b == "Download a PDF version of this wiki page" ) y then Just $ "http://en.wikipedia.org" ++ snd ( y !! 0 ) else Nothing parse :: [ Tag String ] -> Maybe String parse [] = Nothing parse ( x : xs ) | isTagOpen x = case parseHelp x of Just s -> Just s Nothing -> parse xs | otherwise = parse xs main = do x <- getLine tags_1 <- fmap parseTags $ getResponseBody =<< simpleHTTP ( getRequest x ) --open url let lst = head . sections ( ~== "<div class=portal id=p-coll-print_export>" ) $ tags_1 url = fromJust . parse $ lst --rendering url putStrLn url tags_2 <- fmap parseTags $ getResponseBody =<< simpleHTTP ( getRequest url ) print tags_2
If you try requesting the URL through some external tool like wget, you will see that Wikipedia does not serve up the result page directly. It actually returns a 302 Moved Temporarily redirect. When entering this URL in a browser, it will be fine, as the browser will follow the redirect automatically. simpleHTTP, however, will not. simpleHTTP is, as the name suggests, rather simple. It does not handle things like cookies, SSL or redirects. You'll want to use the Network.Browser module instead. It offers much more control over how the requests are done. In particular, the setAllowRedirects function will make it automatically follow redirects. Here's a quick and dirty function for downloading an URL into a String with support for redirects: import Network.Browser grabUrl :: String -> IO String grabUrl url = fmap (rspBody . snd) . browse $ do -- Disable logging output setErrHandler $ const (return ()) setOutHandler $ const (return ()) setAllowRedirects True request $ getRequest url