fix: 3a != a3

Description:
When a number multiplies a variable, the multiply symbol will be automatically added during compiling.
But when a variable multiplies a number, the symbol won't be added.
e.g. `3a != a3`

src/compiler/Compiler.ts

@@ -142,6 +142,10 @@ export default class Compiler {
                         this.pushExponential(i) && i++;
                     } else {
                         this.pushVariable(symbol);
+
+                        if(Is.variable(symbol) && Is.number(this.raw[i + 1], this.isProgrammingMode)) {
+                            this.pushOperator(Operator.MUL);
+                        }
                     }
                     continue;
                 }
@@ -338,9 +342,9 @@ export default class Compiler {
             }
         }
 
-        if(process.env.NODE_ENV === "test") {
+        if(process.env.NODE_ENV === "development") {
             console.log(
-                this.raw.join(""),
+                this.raw,
                 "\n",
                 this.root
             );

src/test/compiler.test.ts

@@ -123,28 +123,42 @@ describe("Compiler tests", () => {
         const f4 = "( 2 a ) b";
         expect(calculate(f4, variables)).toBe("130");
 
-        const f5 = "( a b ) 2";
+        const f5 = "( a 2 ) b";
         expect(calculate(f5, variables)).toBe("130");
 
-        const f6 = "2 e \\pi";
-        expect(calculate(f6)).toBe("17.07946844534713");
+        const f6 = "( a b ) 2";
+        expect(calculate(f6, variables)).toBe("130");
 
-        const f7 = "2 ( e \\pi )";
-        expect(calculate(f7)).toBe("17.07946844534714");
+        const f7 = "2 e \\pi";
+        expect(calculate(f7)).toBe("17.07946844534713");
 
-        const f8 = "( 2 e ) \\pi";
-        expect(calculate(f8)).toBe("17.07946844534713");
+        const f8 = "2 ( e \\pi )";
+        expect(calculate(f8)).toBe("17.07946844534714");
 
-        const f9 = "( e \\pi ) 2";
-        expect(calculate(f9)).toBe("17.07946844534714");
+        const f9 = "( 2 e ) \\pi";
+        expect(calculate(f9)).toBe("17.07946844534713");
 
-        const f10 = "2 ^2 e";
-        expect(calculate(f10)).toBe("10.87312731383618");
+        const f10 = "( e \\pi ) 2";
+        expect(calculate(f10)).toBe("17.07946844534714");
+
+        const f11 = "2 ^2 e";
+        expect(calculate(f11)).toBe("10.87312731383618");
+
+        const f12 = "3 1 b";
+        expect(calculate(f12, variables)).toBe("403");
+
+        const f13 = "b 3 1";
+        expect(calculate(f13, variables)).toBe("403");
     });
 
     test("Integrated Calculations", () => {
-        const f1 = "1 1 4 + 5 1 4 × ( 1 5 7 + 2 4 6 - 3 / ( 2 9 - 2 8 + 1 3 \\sin( \\pi / 6 ) ^2 - \\text{mean}( 1 , 2 , 3 , ( 2 3 - 1 2 ) + | - 1 5 | ^2 - 3 ! ^2 + 4 ! ) ) ) + \\ln( e )";
-        expect(calculate(f1)).toBe("207285.95774647893");
+        const variables = new Map([
+            ["a", "57"],
+            ["b", "15"],
+        ]);
+
+        const f1 = "a 2 + 5 1 4 × ( 1 5 7 + 2 4 6 - 3 / ( 2 9 - 2 8 + 1 3 \\sin( \\pi / 6 ) ^2 - \\text{mean}( 1 , 2 , 3 , ( 2 3 - 1 2 ) + | - b | ^2 - 3 ! ^2 + 4 ! ) ) ) + \\ln( e )";
+        expect(calculate(f1, variables)).toBe("207285.95774647893");
     });
 
 });