add Half and decompose

Author: cscherrer

src/MeasureBase.jl

@@ -30,7 +30,7 @@ Methods for computing density relative to other measures will be
 """
 function logdensity end
 
-
+include("combinators/half.jl")
 include("exp.jl")
 include("domains.jl")
 include("utils.jl")

src/combinators/half.jl

@@ -0,0 +1,5 @@
+export Half
+
+struct Half{M} <: AbstractMeasure
+    μ::M
+end

src/macros.jl

@@ -269,7 +269,11 @@ function _half(__module__, ex)
                 function Base.rand(rng::AbstractRNG, T::Type, μ::$halfdist)
                     return abs(rand(rng, T, unhalf(μ)))
                 end
-                
+                 
+                function decompose(μ::$halfdist)
+                    return Half($dist)
+                end
+
                 (::$halfdist ≪ ::Lebesgue{ℝ₊}) = true
             end
         end