fix issue #717

Author: karlwessel

src/types.jl

@@ -1538,7 +1538,7 @@ function ^(a::SN, b)
     if b isa Number && iszero(b)
         # fast path
         1
-    elseif b isa Number && b < 0
+    elseif b isa Real && b < 0
         Div(1, a ^ (-b))
     elseif ismul(a) && b isa Number
         coeff = unstable_pow(a.coeff, b)

test/basics.jl

@@ -375,6 +375,13 @@ end
     @test isequal(x / -1, -x)
 end
 
+@testset "pow" begin
+    @syms x
+
+    # issue 717
+    @test isequal(Pow(x, im), x^im)
+end
+
 @testset "LiteralReal" begin
     @syms x::LiteralReal y::LiteralReal z::LiteralReal
     @test repr(x+x) == "x + x"