So I'm working through some initial chapter exercise of Real World Haskell and I wanted to know if there is an option in GHCi to make it show function evaluation with parameters on each recursive call. So for example I wrote a simple version of 'map', and when I apply it, I would like GHCi to display each recursive call with actual argum...
Consider the following test function:
testError :: (Error e, MonadError e m) => Bool -> m ()
testError True = return ()
testError False = throwError $ strMsg "hello world"
At the GHCi prompt, I can do the following:
*Main> testError False :: Either String ()
Left "hello world"
*Main> testError True :: Either String ()
Right ()
Bec...
Hi,
I'm using ghci 6.8.2 on Ubuntu. Does ghci use a configuration file where we can do some initial setup?. E.g.: :set prompt "ghci> ".
Thanks,
Roberto.
...
In GHCi:
Prelude> (+3) 2
5
Prelude> (*3) 2
6
Prelude> (/3) 2
0.6666666666666666
Prelude> (-3) 2
No instance for (Num (t -> t1))
arising from the literal 3' at <interactive>:1:2
Possible fix: add an instance declaration for (Num (t -> t1))
In the expression: 3
In the expression: (- 3) 2
In the definit...
Specs
GHC 6.12.1
Mac OS X 10.6.4 x64
MacBook Pro
Problem
I'm having trouble using let syntax. The following code refuses to compile:
module Main where
main = let x = 1
y = 2
z = 3
in putStrLn $ "X = " ++ show x ++ "\nY = " ++ show y ++ "\nZ = " ++ show z
I tried tabbing in y = 2 and z = 3 even more. No dice.
...
When I use GHCi, I almost always end up importing Control.Applicative, Data.List, etc. . Is there a way to configure GHCi to automatically import those modules.
Also, after importing them, how do I keep the prompt from being insanely long?
Prelude Control.Applicative Data.List Database.HDBC Database.HDBC.Sqlite3 System.Directory>
...
I'm writing my first big project in Haskell and I'd like to split it across multiple files. So far, I have written two modules, Parse and Eval. I'd like to have a Main module that just includes these two modules and specifies the main function. I have the files Main.hs, Parse.hs, and Eval.hs and import them in Main, but this happens:
Pr...
I'm following a tutorial. (Real World Haskell)
And I have one beginner question about head and tail called on empty lists: In GHCi it returns exception.
Intuitively I think I would say they both should return an empty list. Could you correct me ? Why not ? (as far as I remember in OzML left or right of an empty list returns nil)
I sur...
I'm used to debug my code using ghci. Often, something like this happens (not so obvious, of course):
ghci> let f@(_:x) = 0:1:zipWith(+)f x
ghci> length f
Then, nothing happens for some time, and if I don't react fast enough, ghci has eaten maybe 2 GB of RAM, causing my system to freeze. If it's too late, the only way to solve this pr...
I am studying Haskell and use Emacs+Haskell mode as my editor.
After playing some simple expressions in GHCi, I am wondering whether these IDE/editor functionality that exist in Visual Stuido for F#:
Can I send the content in the clipboard into the interpreter? Currently I can only :load the file into the interpreter. This is inconv...
While commenting on new features in ghci I wished that ghci had the ability to declare type declaration and declaring new ADT types, someone informed that it was indeed possible, and after searching I found
this page which told me I could do
let numUniques' :: (Eq a) => [a] -> Int; numUniques' = length . nub
Apparently that same sort...
Is there a way to specify the package name for a module for the :browse, :load or :module commands in ghci (version 6.12.1) ?
Some module names are ambiguous:
Prelude> :module Control.Monad.Cont
<no location info>:
Ambiguous module name `Control.Monad.Cont':
it was found in multiple packages: mtl-1.1.0.2 monads-fd-0.1.0.2
...
Hi,
When working in the ocaml or ghci toplevels I often build up a significant "context" for want of a better word, values bound, functions, modules loaded, and so on. Is there a way to save all of that and reload it later so I can continue exactly where I left off? Or better yet, dump out the entire lot as a text file that could be rel...