Forcing the type to be IO {} instead of IO() causes a "panic! The impossible has happened" output.

Below is the source code in which the bug occurs. It is easily reproduce-able, by having the type be IO{} instead of IO().

When ran, this code will produce the "panic! The impossible has happened" output. Which told me to report the bug here.

By changing IO() to IO{} (which I did by accident), no exception is thrown, it simply tells the user to panic!

    main :: IO {}
    main = do
            e1 <- getLine
            e2 <- getLine
            print ((read e1) + (read e2))

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import labels

Attached file IO Monad error.hs ($979).

I can't reproduce your crash. Can you show exact output and which compiler you are using? Like this:

bash$ ghc -c T9077.hs

T9077.hs:3:12: Record syntax is illegal here: {}

bash$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.2

bash$ cat T9077.hs
module Main where

main :: IO {}
main = do
            e1 <- getLine
            e2 <- getLine
            print ((read e1) + (read e2))

I speculate that you are not using 7.8.2.

closed

GHC 7.6.3 indeed panics on the given example, but 7.8.3 does not.

$ ghc-7.8.3 T9077.hs 
[1 of 1] Compiling Main             ( T9077.hs, T9077.o )

T9077.hs:1:12: Record syntax is illegal here: {}

Westycoot: please reopen if you're still having problems.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedWorksForMe

Trac metadata

Trac field	Value
Test case	→ rename/should_fail/T9077

mentioned in commit 13817f06

added compiler perf label

added Pnormal label