well i understand the difficulty, i just pos because ,really some times i get incredible help that i coulmdn not even think it possible.

i admit the code is and the database connection is a stop help.

for the database i cannot do ,for the code i commented a lot  and i can resume with this concise code that recreate the problem:

it's quite simple i noticed that after one lines (see in code the lines and the upper case comments) the query to DB in getAlphaDelta does not works anymore (as it worked before ) but other functions making queries works that what is strange...

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}

import Database.MySQL.Simple
import Database.MySQL.Simple.QueryResults
import Database.MySQL.Simple.Result

import Database.MySQL.Simple.QueryParams
import Database.MySQL.Simple.Param


import Control.Monad
import qualified Data.Text as Tx
import Debug.Trace
import Data.Maybe as Maybe
import Text.Read
import Data.Tuple.Extra

getAlphaDelta :: Connection -> String -> IO (Double,Double)
getAlphaDelta conn name = do
            let qry_head_AlphaDelta_AngularDistance = "select alpha,delta from AngularDistance where Nom = ?" :: Query
            (alpha_delta_rows :: [(Double,Double)]) <- query conn qry_head_AlphaDelta_AngularDistance (Only (name::String))
            return (head alpha_delta_rows)

main :: IO ()

main =

  do
    conn <- connect defaultConnectInfo
      { connectHost = "moita",
        connectUser = "mattei",
        connectPassword = "sidonie2",
        connectDatabase = "sidonie" }


-- check getAlphaDelta works:

-- HERE getAlphaDelta WORKS

    let name = "WOR   7"
    putStrLn $ show name
    ad <- getAlphaDelta conn name
    putStr "ad ="
    putStrLn $ show ad

    (names ::[Only Tx.Text])<- query_ conn "SELECT Nom FROM AngularDistance WHERE distance > 0.000278"

-- AFTER THE PREVIOUS LINE getAlphaDelta WILL NOT WORKS AND ISSUE A SEGFAULT IN GHCI

    let name3 = "A     7"
    putStrLn $ show name3
    ad3 <- getAlphaDelta conn name3
    putStr "ad3 ="
    putStrLn $ show ad3

close conn

here is the output:

[mattei@localhost Haskell]$ ghci
GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
Prelude> :load UpdateSidonie.hs
[1 of 1] Compiling Main             ( UpdateSidonie.hs, interpreted )
Ok, one module loaded.
*Main> main
"WOR   7"
ad =(17386.0,7120.0)
"A     7"
Segmentation fault (core dumped)

as you see the first call to getAlphaDelta is ok but the second issue a Segmentation fault.

i will try now with ghci 8.4 .... and hiope to give you some news...

Damien

On Thu, Feb 21, 2019 at 8:15 PM Sven Panne <svenpanne@gmail.com> wrote:

Am Do., 21. Feb. 2019 um 19:22 Uhr schrieb Damien Mattei <damien.mattei@gmail.com>:

i had attached the whole file, so anyone can read the whole code, perheaps it could help, saying me if there is compilation error on other ghc versions, with mine no error at compilation.

I very much doubt that anyone likes to read >500 lines of Haskell code with lots of external dependencies to help you with your problem. A good hint for Open Source SW in general: If you think you might have found a bug, cut down your example as much as possible, throw out as many external dependencies as you can while still reproducing your problem, then, and only then, post it to other people. You simply can't expect that other people will do that debugging work for you in their spare time. The code you post doesn't really have to make sense, it should just be the minimum amount of code needed to reproduce the problem.

In a nutshell: The probability that you get some help is inversely proportional to the size of your example, and even more inversely proportional to the number of external dependencies (libraries etc.).

 

The problem to test is that without the database connection which is behind a firewall of course ,the code can not be executed. [...]

Well, that is basically a show stopper for getting help... 

 I don't want to be mean, quite the opposite: I just want to explain why you probably won't receive any help in the current form. This is not special to the Haskell community, the situation would be very much the same if you posted an equivalent problem of similar size to the Racket/Python/... community. I'm quite sure that most maintainer would be happy to have a look e.g. at a program consisting of a dozen lines without external dependencies.