lazy evaluation of rational powers

src/types.jl

@@ -608,7 +608,15 @@ function basicsymbolic(f, args, stype, metadata)
             end
             res
         elseif f == (^) && length(args) == 2
-            res = args[1] ^ args[2]
+            if args[2] isa Rational && !isa(args[1], Symbolic)
+                if isinteger(args[2])
+                    res = args[1] ^ numerator(args[2])
+                else
+                    @goto FALLBACK
+                end
+            else
+                res = args[1] ^ args[2]
+            end
             if ispow(res)
                 @set! res.metadata = metadata
             end
@@ -1210,9 +1218,20 @@ function ^(a::SN, b)
     elseif b isa Number && b < 0
         Div(1, a ^ (-b))
     elseif ismul(a) && b isa Number
-        coeff = unstable_pow(a.coeff, b)
+        new_dict = mapvalues((k, v) -> b*v, a.dict)
+        if b isa Rational
+            if isinteger(b)
+                coeff = a.coeff ^ numerator(b)
+            else
+                coeff = 1
+                new_dict[term(^, a.coeff, b)] = 1
+            end
+        else
+            coeff = unstable_pow(a.coeff, b)
+        end
+
         Mul(promote_symtype(^, symtype(a), symtype(b)),
-            coeff, mapvalues((k, v) -> b*v, a.dict))
+            coeff, new_dict)
     else
         Pow(a, b)
     end

test/basics.jl

@@ -363,5 +363,23 @@ end
     ax = adjoint(x)
     @test isequal(ax, x)
     @test ax === x
-    @test isequal(adjoint(y), conj(y)) 
+    @test isequal(adjoint(y), conj(y))
+end
+
+@testset "pow" begin
+    @syms x y
+    @eqtest (2x)^(1//2) == term(^, 2, 1//2) * x^(1//2)
+    @eqtest (2x)^(1//1) == 2x
+    # @eqtest (2x)^1 == 2x ## This currently fails and returns (2//1)*x
+    @eqtest (2x)^(2//1) == 4x^(2//1)
+    @eqtest ((1//3)*x)^(1//4) == term(^, 1//3, 1//4) * x^(1//4)
+
+    @eqtest (x+y)^(1//2) == (x+y)^(1//2)
+    @eqtest (x+y)^(1//1) == x+y
+
+    @eqtest (x^(3//1))^(1//3) == x
+    @eqtest (x^(3//1))^(2//3) == x^(2//1)
+    @eqtest (x^(2//1))^2 ==  x^(4//1)
+
+    @test ((2x)^0.5).coeff ≈ sqrt(2)
 end

test/rulesets.jl

@@ -52,6 +52,14 @@ end
     @test simplify(Term(zero, [a])) == 0
     @test simplify(Term(zero, [b + 1])) == 0
     @test simplify(Term(zero, [x + 2])) == 0
+
+    @eqtest simplify(Term(sqrt, [2])) == Term(sqrt, [2])
+    @eqtest simplify(Term(^, [2, 1//2])) == Term(^, [2, 1//2])
+    @eqtest simplify(Term(^, [2x, 1//2])) == Term(^, [2, 1//2]) * x^(1//2)
+    @test simplify(Term(^, [2, 3])) ≈ 8
+    @test simplify(Term(^, [1//3, 3])) == 1//27
+    @test simplify(Term(^, [2, 0.5])) ≈ 2^0.5
+    @test simplify(Term(^, [2.5, 0.25])) ≈ 2.5^(0.25)
 end
 
 @testset "LiteralReal" begin