[julia-users] Inheriting from Real works, from AbstractFloat does not?

[Jeffrey Sarnoff]

julia> immutable SubtypeReal <: Real
           val::Float64
       end

julia> a=SubtypeReal(5.0)
SubtypeReal(5.0)

julia> immutable SubtypeAbsFloat <: AbstractFloat
           val::Float64
       end

julia> a=SubtypeAbsFloat(5.0)
Error showing value of type SubtypeAbsFloat:
ERROR: - not defined for SubtypeAbsFloat
 in _show at grisu.jl:64
 in show at grisu.jl:119
 ...
 in run_repl at ./REPL.jl:166
 in _start at ./client.jl:453

Defining show for it does not help.