refactor(kernel/expr): remove code duplication
refactor(kernel/expr): remove code duplication

soonhokong/lean-windows,leanprover/lean,soonhokong/lean-windows,fgdorais/lean,soonhokong/lean-osx,dselsam/lean,fgdorais/lean,fpvandoorn/lean,levnach/lean,fgdorais/lean,dselsam/lean,leanprover/lean,Kha/lean,javra/lean,rlewis1988/lean,javra/lean,levnach/lean,c-cube/lean,rlewis1988/lean,leodemoura/lean,fgdorais/lean,leanprover/lean,fpvandoorn/lean2,Kha/lean,avigad/lean,dselsam/lean,digama0/lean,c-cube/lean,fpvandoorn/lean,soonhokong/lean,eigengrau/lean,leanprover-community/lean,digama0/lean,leanprover-community/lean,johoelzl/lean,sp3ctum/lean,avigad/lean,rlewis1988/lean,fpvandoorn/lean,sp3ctum/lean,htzh/lean,avigad/lean,avigad/lean,UlrikBuchholtz/lean,fpvandoorn/lean,eigengrau/lean,soonhokong/lean-osx,htzh/lean,leanprover-community/lean,digama0/lean,johoelzl/lean,leodemoura/lean,soonhokong/lean,leodemoura/lean,levnach/lean,soonhokong/lean,javra/lean,digama0/lean,javra/lean,dselsam/lean,Kha/lean,leanprover-community/lean,leanprover/lean,fpvandoorn/lean2,leanprover-community/lean,fgdorais/lean,levnach/lean,sp3ctum/lean,sp3ctum/lean,c-cube/lean,Kha/lean,rlewis1988/lean,dselsam/lean,fpvandoorn/lean2,soonhokong/lean-windows,soonhokong/lean-osx,johoelzl/lean,digama0/lean,UlrikBuchholtz/lean,Kha/lean,c-cube/lean,htzh/lean,UlrikBuchholtz/lean,sp3ctum/lean,fpvandoorn/lean2,leodemoura/lean,eigengrau/lean,leodemoura/lean,Kha/lean,soonhokong/lean-windows,htzh/lean,fgdorais/lean,soonhokong/lean-osx,htzh/lean,UlrikBuchholtz/lean,leanprover/lean,soonhokong/lean-osx,fpvandoorn/lean,c-cube/lean,johoelzl/lean,leanprover-community/lean,avigad/lean,fpvandoorn/lean,fpvandoorn/lean2,johoelzl/lean,johoelzl/lean,eigengrau/lean,digama0/lean,rlewis1988/lean,dselsam/lean,javra/lean,soonhokong/lean-windows,leanprover/lean,levnach/lean,soonhokong/lean,UlrikBuchholtz/lean,soonhokong/lean,rlewis1988/lean,eigengrau/lean,avigad/lean,leodemoura/lean