Are you sure...
# LC_ALL=C pacman -S haskell-sandi
resolving dependencies...
looking for conflicting packages...
Packages (1) haskell-sandi-0.5-91
Total Download Size: 0.07 MiB
Total Installed Size: 0.45 MiB
Net Upgrade Size: 0.00 MiB
:: Proceed with installation? [Y/n] y
:: Retrieving packages...
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from ftp.icm.edu.pl : The requested URL returned error: 404
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from ftp.icm.edu.pl : The requested URL returned error: 404
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from arch.midov.pl : The requested URL returned error: 404
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from arch.nixlab.pl : The requested URL returned error: 404
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from arch.nixlab.pl : The requested URL returned error: 404
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from mirror.onet.pl : The requested URL returned error: 404
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from piotrkosoft.net : The requested URL returned error: 404
warning: failed to retrieve some files
error: failed to commit transaction (failed to retrieve some files)
Errors occurred, no packages were upgraded.
I should say that i had similar problem while installing obarun... I had polish mirrors on in mirrorlist. Imagemagick was problematic to download, it had the same error 404... I changed mirrors to worldwide and imagemagick downloaded.
But with this haskell sandi even downloading from worldwide fails.
# LC_ALL=C pacman -Sy haskell-sandi
:: Synchronizing package databases...
obcore is up to date
obextra is up to date
obcommunity is up to date
obmultilib-testing is up to date
obmultilib is up to date
observice is up to date
core is up to date
extra is up to date
community-testing is up to date
community is up to date
resolving dependencies...
looking for conflicting packages...
Packages (1) haskell-sandi-0.5-91
Total Download Size: 0.07 MiB
Total Installed Size: 0.45 MiB
Net Upgrade Size: 0.00 MiB
:: Proceed with installation? [Y/n] y
:: Retrieving packages...
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from mirrors.evowise.com : The requested URL returned error: 404
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from mirror.rackspace.com : The requested URL returned error: 404
error: failed retrieving file 'haskell-sandi-0.5-91-x86_64.pkg.tar.zst' from mirror.rackspace.com : The requested URL returned error: 404
warning: failed to retrieve some files
error: failed to commit transaction (failed to retrieve some files)
Errors occurred, no packages were upgraded.