Install this version:
emerge -a =dev-haskell/mtl-2.3.2
If this version is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask =dev-haskell/mtl-2.3.2
Or alternatively:
emerge --autounmask-write -a =dev-haskell/mtl-2.3.2
# Copyright 1999-2026 Gentoo Authors
# Distributed under the terms of the GNU General Public License v2
EAPI=8
# ebuild generated by hackport 0.9.1.0.9999
CABAL_HACKAGE_REVISION=1
CABAL_FEATURES="lib profile haddock hoogle hscolour"
# break circular dependencies:
# https://github.com/gentoo-haskell/gentoo-haskell/issues/810
CABAL_FEATURES+=" nocabaldep"
inherit haskell-cabal
DESCRIPTION="Monad classes for transformers, using functional dependencies"
HOMEPAGE="https://github.com/haskell/mtl"
LICENSE="BSD"
SLOT="0/${PV}"
KEYWORDS="~amd64 ~arm64"
RDEPEND=">=dev-lang/ghc-9.0.2:=
"
DEPEND="${RDEPEND}
>=dev-haskell/cabal-3.4.1.0
"
CABAL_CORE_LIB_GHC_PV="9.12.4"
>=dev-lang/ghc-9.0.2:= >=dev-haskell/cabal-3.4.1.0
>=dev-lang/ghc-9.0.2:=