Fix anonymous argument with type parameter

Author: devmotion

Project.toml

@@ -1,6 +1,6 @@
 name = "DynamicPPL"
 uuid = "366bfd00-2699-11ea-058f-f148b4cae6d8"
-version = "0.17.9"
+version = "0.17.10"
 
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"

src/compiler.jl

@@ -262,7 +262,7 @@ function build_model_info(input_expr)
     # Extract the names of the arguments.
     allargs_syms = map(allargs_exprs) do arg
         MacroTools.@match arg begin
-            (::Type{T_}) | (name_::Type{T_}) => T
+            (::S_{T_}) | (name_::Type{T_}) => T
             name_::T_ => name
             x_ => x
         end

test/compiler.jl

@@ -602,4 +602,10 @@ end
         @test !DynamicPPL.hasmissing(Matrix{Real})
         @test !DynamicPPL.hasmissing(Vector{Matrix{Float32}})
     end
+
+    @testset "issue #393: anonymous argument with type parameter" begin
+        @model f_393(::Val{ispredict}=Val(false)) where {ispredict} = ispredict ? 0 : 1
+        @test f_393()() == 1
+        @test f_393(Val(true))() == 0
+    end
 end