Missing build tools

[berberman]

Target: BNFC

PKGBUILD:

depends=('ghc-libs' 'haskell-semigroups')
makedepends=('ghc' 'haskell-hunit' 'haskell-quickcheck' 'haskell-doctest' 'haskell-hspec' 'haskell-temporary')

Build log:

==> Starting build()...
Configuring BNFC-2.8.4...
Setup: The program 'alex' is required but it could not be found.

==> ERROR: A failure occurred in build().