Package: ghc Version: 8.8.1+dfsg2-1~exp1 Dear Maintainer,
When ":print length" is run at the GHCi prompt, the 'impossible'
happens:
$ ghci
GHCi, version 8.8.1: https://www.haskell.org/ghc/ :? for help
Prelude> :print length
ghc: panic! (the 'impossible' happened)
(GHC version 8.8.1 for x86_64-unknown-linux):
isUnliftedType
t1_a1w0[rt] :: TYPE t0_a1vZ[rt]
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/utils/Outputable.hs:1159:37 in
ghc:Outputable
pprPanic, called at compiler/types/Type.hs:2278:10 in ghc:Type
Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug
This does not happen with all functions. In fact, length is the only
function I have found so far that does this. If I define my own version
of length, len, this bug does not appear:
Prelude> :{
Prelude| len l = case l of
Prelude| [] -> 0
Prelude| (x:xs) -> 1 + len xs
Prelude| :}
Prelude> :print len
len = (_t1::Num p => [a] -> p)
So, maybe length is defined in C code in the compiler rather than an
actual Haskell function, and that is what triggers the bug?
I've also tested this in version ghc_8.8.1+dfsg1+is+8.6.5+dfsg1-2 (the
current latest in testing) with the same results.
Related: #914702 (however, that bug seems to be fixed in both the
versions I tried).
Thanks,
Asher
--
Steal this tagline. I did.
GPG fingerprint: 38F3 975C D173 4037 B397 8095 D4C9 C4FC 5460 8E68
-- System Information:
Debian Release: bullseye/sid
APT prefers testing
APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Kernel: Linux 5.3.0-2-amd64 (SMP w/2 CPU cores)
Kernel taint flags: TAINT_FIRMWARE_WORKAROUND
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8),
LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled
Versions of packages ghc depends on:
ii dpkg 1.19.7
ii gcc 4:9.2.1-3.1
ii libbsd-dev 0.10.0-1
ii libc6 2.29-3
ii libc6-dev 2.29-3
ii libffi-dev 3.2.1-9
ii libffi6 3.2.1-9
ii libgmp-dev 2:6.1.2+dfsg-4
ii libgmp10 2:6.1.2+dfsg-4
ii libncurses-dev [libncurses5-dev] 6.1+20191019-1
ii libncurses5-dev 6.1+20191019-1
ii libtinfo6 6.1+20191019-1
ghc recommends no packages.
Versions of packages ghc suggests:
it ghc-doc 8.8.1+dfsg1+is+8.6.5+dfsg1-2
pn ghc-prof <none>
ii haskell-doc 20061128
ii llvm-7 1:7.0.1-9+b2
ii perl 5.30.0-9
-- no debconf information
signature.asc
Description: PGP signature
