fix 1-arg printing when op is also a binaryoperator

Author: shashi

src/types.jl

@@ -320,6 +320,7 @@ function Base.show(io::IO, t::Term)
         if binary
             get(io, :paren, false) && Base.printstyled(io, "(",color=color)
             for i = 1:length(args)
+                length(args) == 1 && Base.printstyled(io, fname, color=color)
                 Base.printstyled(IOContext(io, :paren => true),
                                  args[i], color=color)
                 i != length(args) && Base.printstyled(io, " $fname ", color=color)

test/basics.jl

@@ -87,3 +87,10 @@ end
     @test substitute(sin(a+b), Dict(a=>1)) == sin(1+b)
     @test substitute(a+b, Dict(a=>1, b=>3)) |> simplify == 4
 end
+
+@testset "printing" begin
+    @syms a b
+    @test repr(a+b) == "a + b"
+    @test repr(-a) == "-a"
+    @test repr(-a + 3) == "3 + (-a)"
+end