  In this paper we construct an "abstract Fock space" for general Lie types
that serves as a generalisation of the infinite wedge $q$-Fock space familiar
in type $A$. Specifically, for each positive integer $\ell$, we define a
$\mathbb{Z}[q,q^{-1}]$-module $\mathcal{F}_{\ell}$ with bar involution by
specifying generators and "straightening relations" adapted from those
appearing in the Kashiwara-Miwa-Stern formulation of the $q$-Fock space. By
relating $\mathcal{F}_{\ell}$ to the corresponding affine Hecke algebra we show
that the abstract Fock space has standard and canonical bases for which the
transition matrix produces parabolic affine Kazhdan-Lusztig polynomials. This
property and the convenient combinatorial labeling of bases of
$\mathcal{F}_{\ell}$ by dominant integral weights makes $\mathcal{F}_{\ell}$ a
useful combinatorial tool for determining decomposition numbers of Weyl modules
for quantum groups at roots of unity.
