Merge pull request #234 from JuliaSymbolics/s/less-parens

Less parens in printing

src/types.jl

@@ -423,13 +423,18 @@ setargs(t, args) = Term{symtype(t)}(operation(t), args)
 cdrargs(args) = setargs(t, cdr(args))
 
 print_arg(io, x::Union{Complex, Rational}) = print(io, "(", x, ")")
-print_arg(io, x) = print(io, x)
-print_arg(io, f::typeof(^), x) = print_arg(IOContext(io, :paren=>true), x)
+function print_arg(io, x; paren=false)
+    if paren && isbinop(x)
+        print(io, "(", x, ")")
+    else
+        print(io, x)
+    end
+end
 print_arg(io, s::String) = show(io, s)
 function print_arg(io, f, x)
     f !== (*) && return print_arg(io, x)
-    if istree(x) && Base.isbinaryoperator(nameof(operation(x)))
-        print_arg(IOContext(io, :paren=>true), x)
+    if Base.isbinaryoperator(nameof(f)) && isbinop(x)
+        print_arg(io, x, paren=true)
     else
         print_arg(io, x)
     end
@@ -448,11 +453,20 @@ function show_add(io, args)
             print_arg(io, -, t)
         else
             print(io, " - ")
-            print_arg(IOContext(io, :paren=>true), +, -t)
+            print_arg(io, -t, paren=true)
         end
     end
 end
 
+isbinop(f) = istree(f) && Base.isbinaryoperator(nameof(operation(f)))
+function show_pow(io, args)
+    base, ex = args
+
+    print_arg(io, base, paren=isbinop(base))
+    print(io, "^")
+    print_arg(io, ex, paren=isbinop(base))
+end
+
 function show_mul(io, args)
     length(args) == 1 && return print_arg(io, *, args[1])
 
@@ -481,8 +495,8 @@ function show_call(io, f, args)
     binary = Base.isbinaryoperator(fname)
     if binary
         for (i, t) in enumerate(args)
-            i != 1 && print(io, fname == :^ ? fname : " $fname ")
-            print_arg(io, (^), t)
+            i != 1 && print(io, " $fname ")
+            print_arg(io, t)
         end
     else
         if f isa Sym
@@ -507,15 +521,15 @@ function show_term(io::IO, t)
     f = operation(t)
     args = arguments(t)
 
-    get(io, :paren, false) && print(io, "(")
     if f === (+)
         show_add(io, args)
     elseif f === (*)
         show_mul(io, args)
+    elseif f === (^)
+        show_pow(io, args)
     else
         show_call(io, f, args)
     end
-    get(io, :paren, false) && print(io, ")")
 
     return nothing
 end