How to define a function in ghci across multiple lines

Posted by Peter McGrattan on Stack Overflow See other posts from Stack Overflow or by Peter McGrattan
Published on 2010-05-17T00:16:14Z Indexed on 2010/05/17 0:20 UTC
Read the original article Hit count: 663

Filed under:

ghci

|

haskell

I'm trying to define any simple function that spans multiple lines in ghci, take the following as an example:

let abs n | n >= 0 = n
          | otherwise = -n

So far I've tried pressing Enter after the first line:

Prelude> let abs n | n >= 0 = n
Prelude>           | otherwise = -n
<interactive>:1:0: parse error on input `|'

I've also attempted to use the :{ and :} commands but I don't get far:

Prelude> :{
unknown command ':{'
use :? for help.

I'm using GHC Interactive version 6.6 for Haskell 98 on Linux, what am I missing?

© Stack Overflow or respective owner

Related posts about ghci

How to define a function in ghci across multiple lines

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to define any simple function that spans multiple lines in ghci, take the following as an example: let abs n | n >= 0 = n | otherwise = -n So far I've tried pressing Enter after the first line: Prelude> let abs n | n >= 0 = n Prelude> | otherwise = -n <interactive>:1:0:… >>> More
GHCi error: Not in scope

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to compile this function from Learn You a Haskell for Great Good. removeNonUppercase st = [ c | c <- st, c `elem` ['A'..'Z']] by placing it into a removeNonUpperCase.hs file. It compiles fine, but when passing the argument: ghci> removeNonUppercase "Hahaha! Ahahaha!" the… >>> More
Info on type family instances

as seen on Stack Overflow - Search for 'Stack Overflow'
Intro: While checking out snoyman's "persistent" library I found myself wanting ghci's (or another tool) assistance in figuring out stuff. ghci's :info doesn't seem to work as nicely with type-families and data-families as it does with "plain" types: > :info Maybe data Maybe a = Nothing | Just… >>> More
Compiled Haskell libraries with FFI imports are invalid when imported into GHCI

as seen on Stack Overflow - Search for 'Stack Overflow'
I am using GHC 6.12.1, in Ubuntu 10.04 When I try to use the FFI syntax for static storage, only modules running in interpreted mode (ie GHCI) work properly. Compiled modules have invalid pointers, and do not work. I'd like to know whether anybody can reproduce the problem, whether this an error… >>> More
Why can't GHCi resolve the kind of [[]] ?

as seen on Stack Overflow - Search for 'Stack Overflow'
Why can't Haskell resolve the kind of [[]] (A list of lists)? Why isn't it simply * - *, as I can give it a type like Int, and get [[Int]], which is of kind *. >>> More

Related posts about haskell

Learning Haskell: How to remove an item from a List in Haskell

as seen on Stack Overflow - Search for 'Stack Overflow'
Trying to learn Haskell. I am trying to write a simple function to remove a number from a list without using built-in function (delete...I think). For the sake of simplicity, let's assume that the input parameter is an Integer and the list is an Integer list. Here is the code I have, Please tell me… >>> More
Using Data.Heap in Haskell, or reading Haskell docs for a beginner

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to use Haskells Data.Heap module, but I'm incapable of even using it with integers. The only heap I've been capable of using is "empty", which does not take any arguments. Later on I'll figure out how to instance for my needs, but for now I'd be glad if I was even able to test it with… >>> More
What kind of things are easy in Haskell and hard in Scala, and vice versa?

as seen on Programmers - Search for 'Programmers'
There has been some intermingling of Scala and Haskell communities, and I have noticed now and then people commenting on stuff that's supposed to be easy in Haskell and hard and Scala. Less often (maybe because I read Scala questions, not Haskell ones), I see someone mentioning that something in Scala… >>> More
Haskell's cabal dependency problem with happy

as seen on Programmers - Search for 'Programmers'
I have problems installing ghc-mod on my linux machine. cabal worries about "happy" not being available in versione = 1.17: $ cabal install ghc-mod Resolving dependencies... [1 of 1] Compiling Main ( /tmp/haskell-src-exts-1.14.0-1357/haskell-src-exts-1.14.0/Setup.hs, /tmp/haskell-src-exts-1… >>> More
Understanding Haskell's fibonacci

as seen on Stack Overflow - Search for 'Stack Overflow'
fibs :: [Int] fibs = 0 : 1 : [ a + b | (a, b) <- zip fibs (tail fibs)] This generates the Fibonacci sequence. I understand the behaviour of the guards, of :, zip and tail, but I don't understand <-. What is it doing here? >>> More