change binomial registration

src/extra_functions.jl

@@ -1,4 +1,37 @@
-@register_symbolic Base.binomial(n, k::Integer)::Int true
+@register_symbolic Base.binomial(n, k)::Int true
+function _binomial(nothing, n, k)
+    begin
+        args = [n, k]
+        unwrapped_args = map(Symbolics.unwrap, args)
+        res = if !(any((x->begin
+                                SymbolicUtils.issym(x) || SymbolicUtils.istree(x)
+                            end), unwrapped_args))
+                Base.binomial(unwrapped_args...)
+            else
+                SymbolicUtils.Term{Int}(Base.binomial, unwrapped_args)
+            end
+        if typeof.(args) == typeof.(unwrapped_args)
+            return res
+        else
+            return Symbolics.wrap(res)
+        end
+    end
+end
+
+for (T1, T2) in ((Symbolics.SymbolicUtils.Symbolic{<:Real}, Int64),
+                 (Num, Int64),
+                 (Real, Symbolics.SymbolicUtils.Symbolic{<:Int64}),
+                 (Symbolics.SymbolicUtils.Symbolic{<:Real}, Symbolics.SymbolicUtils.Symbolic{<:Int64}),
+                 (Num, Symbolics.SymbolicUtils.Symbolic{<:Int64}))
+
+    @eval function Base.binomial(n::$T1, k::$T2)
+        if any(Symbolics.iswrapped, (n, k))
+            Symbolics.wrap(_binomial(nothing, Symbolics.unwrap(n), Symbolics.unwrap(k)))
+        else
+            _binomial(nothing, n, k)
+        end
+    end
+end
 
 @register_symbolic Base.sign(x)::Int
 derivative(::typeof(sign), args::NTuple{1,Any}, ::Val{1}) = 0

test/overloads.jl

@@ -237,3 +237,18 @@ for f in [<, <=, >, >=, isless]
 end
 
 @test_nowarn binomial(t, 1)
+
+# test for https://github.com/JuliaSymbolics/Symbolics.jl/issues/1028
+let
+    @variables t A(t) B
+    @test try binomial(A, 2*B^2)
+        true
+    catch
+        false
+    end
+    @test try binomial(Symbolics.value(A), Symbolics.value(2*B^2))
+        true
+    catch
+        false
+    end
+end