make quantile function of truncated distributions accept more than just Float64 arguments (#660)

* Changed the required argument type of the truncated distribution's quantile function from `::Float64` to the more general `::Real`

* rather use subtype of  than  itself

* added tests

Author: jleugeri

src/truncate.jl

@@ -47,7 +47,7 @@ insupport(d::Truncated{D,Union{Discrete,Continuous}}, x::Real) where {D<:Univari
 
 ### evaluation
 
-quantile(d::Truncated, p::Float64) = quantile(d.untruncated, d.lcdf + p * d.tp)
+quantile(d::Truncated, p::Real) = quantile(d.untruncated, d.lcdf + p * d.tp)
 
 for f in [:pdf, :logpdf, :cdf, :logcdf, :ccdf, :logccdf]
     @eval ($f)(d::Truncated, x::Int) = ($f)(d, float(x))

test/truncate.jl

@@ -84,6 +84,12 @@ function verify_and_test(d::UnivariateDistribution, dct::Dict, n_tsamples::Int)
         # @test isapprox(cdf(d, Dual(x))   , cf, atol=sqrt(eps()))
     end
 
+    # test if truncated quantile function can be evaluated consistently for different types at certain points
+    @test isapprox(quantile(d, 0), quantile(d, Float32(0)))
+    @test isapprox(quantile(d, 1), quantile(d, Float32(1.0)))
+    @test isapprox(quantile(d, Float64(0.3)), quantile(d, Float32(0.3)))
+    @test isapprox(quantile(d, Float64(0.7)), quantile(d, Float32(0.7)))
+
     try
         m = mgf(d,0.0)
         @test m == 1.0