use fix and fix some errors

src/abstractprobprog.jl

@@ -131,20 +131,19 @@ end
         params,
     ) -> T
 
-Draw a sample from the joint distribution specified by `model` conditioned on the values in
-`params`.
+Draw a sample from the predictive distribution specified by `model` with its parameters fixed to `params`.
 
 The sample will be returned as format specified by `T`.
 """
-function StatsBase.predict(rand::AbstractRNG, T::Type, model::AbstractProbabilisticProgram, params)
-    return rand(rng, T, condition(model, params))
+function StatsBase.predict(rng::AbstractRNG, T::Type, model::AbstractProbabilisticProgram, params)
+    return rand(rng, T, fix(model, params))
 end
 function StatsBase.predict(T::Type, model::AbstractProbabilisticProgram, params)
     return StatsBase.predict(Random.default_rng(), T, model, params)
 end
 function StatsBase.predict(model::AbstractProbabilisticProgram, params)
     return StatsBase.predict(NamedTuple, model, params)
 end
-function StatsBase.predict(rng::AbstractRNG, params)
+function StatsBase.predict(rng::AbstractRNG, T::Type, model::AbstractProbabilisticProgram, params)
     return StatsBase.predict(rng, NamedTuple, model, params)
 end