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Running GHC 9.1 - IntelliSense is not available

Your code is run with runghc solution.hs. Your code runs in interpreted mode, so you don’t need a special entrypoint or anything.

We have a couple testing options available. Simple tests using Hspec are straightforward:

import Test.Hspec
import Test.QuickCheck
import Control.Exception (evaluate)

main :: IO ()
main = hspec $ do
  describe "Prelude.head" $ do
    it "returns the first element of a list" $ do
      head [23 ..] `shouldBe` (23 :: Int)

    it "returns the first element of an *arbitrary* list" $
      property $ \x xs -> head (x:xs) == (x :: Int)

    it "throws an exception if used with an empty list" $ do
      evaluate (head []) `shouldThrow` anyException
Code language: Haskell (haskell)

You can also use QuickCheck’s more powerful test generation framework directly (this test fails):

import Test.QuickCheck

prop_revapp :: [Int] -> [Int] -> Bool
prop_revapp xs ys = reverse (xs++ys) == reverse xs ++ reverse ys

main = quickCheck prop_revapp
Code language: Haskell (haskell)

We install a variety of packages in the Haskell environment (including req for HTTP requests). The output of cabal list --installed --simple is below:

Cabal 2.4.0.1
HUnit 1.6.0.0
QuickCheck 2.13.1
RSA 2.3.1
SHA 1.6.4.4
aeson 1.4.3.0
ansi-terminal 0.9.1
array 0.5.3.0
asn1-encoding 0.9.5
asn1-parse 0.9.4
asn1-types 0.3.2
async 2.2.1
attoparsec 0.13.2.2
attoparsec-iso8601 1.0.1.0
authenticate-oauth 1.6
base 4.12.0.0
base-compat 0.10.5
base-orphans 0.8.1
base64-bytestring 1.0.0.2
basement 0.0.10
binary 0.8.6.0
blaze-builder 0.4.1.0
bytestring 0.10.8.2
cabal-doctest 1.0.6
call-stack 0.1.0
case-insensitive 1.2.1.0
cereal 0.5.8.0
clock 0.8
colour 2.3.5
connection 0.3.0
containers 0.6.0.1
cookie 0.4.4
crypto-api 0.13.3
crypto-pubkey-types 0.4.3
cryptonite 0.25
data-default 0.7.1.1
data-default-class 0.1.2.0
data-default-instances-containers 0.0.1
data-default-instances-dlist 0.0.1
data-default-instances-old-locale 0.0.1
deepseq 1.4.4.0
directory 1.3.3.0
dlist 0.8.0.6
entropy 0.4.1.4
exceptions 0.10.2
filepath 1.4.2.1
ghc 8.6.5
ghc-boot 8.6.5
ghc-boot-th 8.6.5
ghc-compact 0.1.0.0
ghc-heap 8.6.5
ghc-prim 0.5.3
ghci 8.6.5
hashable 1.2.7.0
hashtables 1.2.3.1
haskeline 0.7.4.3
hourglass 0.2.12
hpc 0.6.0.3
hspec 2.7.1
hspec-core 2.7.1
hspec-discover 2.7.1
hspec-expectations 0.8.2
http-api-data 0.4
http-client 0.6.4
http-client-tls 0.3.5.3
http-types 0.12.3
integer-gmp 1.0.2.0
integer-logarithms 1.0.3
libiserv 8.6.3
memory 0.14.18
mime-types 0.1.0.9
monad-control 1.0.2.3
mtl 2.2.2
network 3.1.0.0
network-uri 2.6.1.0
old-locale 1.0.0.7
parsec 3.1.13.0
pem 0.2.4
pretty 1.1.3.6
primitive 0.6.4.0
process 1.6.5.0
quickcheck-io 0.2.0
random 1.1
req 2.0.1
retry 0.8.0.1
rts 1.0
scientific 0.3.6.2
setenv 0.1.1.3
socks 0.6.0
split 0.2.3.3
splitmix 0.0.2
stm 2.5.0.0
streaming-commons 0.2.1.0
tagged 0.8.6
template-haskell 2.14.0.0
terminfo 0.4.1.2
text 1.2.3.1
tf-random 0.5
th-abstraction 0.3.1.0
time 1.8.0.2
time-locale-compat 0.1.1.5
tls 1.4.1
transformers 0.5.6.2
transformers-base 0.4.5.2
transformers-compat 0.6.5
unix 2.7.2.2
unordered-containers 0.2.10.0
uuid-types 1.0.3
vector 0.12.0.3
vector-algorithms 0.8.0.1
x509 1.7.5
x509-store 1.6.7
x509-system 1.6.6
x509-validation 1.6.11
xhtml 3000.2.2.1
zlib 0.6.2
Code language: Haskell (haskell)

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