Improvement: ability to compare literal strings given in expressions.

Author: ws-garcia

README.md

@@ -37,7 +37,7 @@ Token         =     [{Unary}] Argument [(Operator | Function) ["("] [{Unary}] [A
 Argument      =     (List | Variable | Operand)
 List          =     "{" ["{"] SubExpr [{";" SubExpr}] ["}"] "}"
 Unary         =     "-" | "+" | ~
-Operand       =     ({Digit} ["."] [{Digit}] ["E"("-" | "+"){Digit}] | (True | False))
+Operand       =     ({Digit} ["."] [{Digit}] ["E"("-" | "+"){Digit}] | (True | False) | "'"Alphabet"'")
 Variable      =     Alphabet [{Decimal}] [{(Digit | Alphabet)}]
 Alphabet      =     "A-Z" | "a-z"
 Decimal       =     "."
@@ -162,6 +162,15 @@ Sub TrigFunctions()
         End If
     End With
 End Sub
+Sub StringComp()
+    Dim Evaluator As VBAexpressions
+    Set Evaluator = New VBAexpressions
+    
+    With Evaluator
+        .Create "Region = 'Central America'"            'Create a expression with `Region` as variable
+        .Eval ("Region = 'Asia'")                       'Assign value to variable and then evaluate
+    End With
+End Sub
 ```
 
 ## Licence

docs/assets/img/VBA Expressions.png

@@ -284,3 +284,21 @@ TestFail:
     Assert.Fail "Test raised an error: #" & err.Number & " - " & err.Description
     Resume TestExit
 End Sub
+'@TestMethod("VBA Expressions")
+Private Sub testStringComp()
+    On Error GoTo TestFail
+    
+    actual = GetResult( _
+                        "Region = 'Central America'" _
+                        , "Region = 'Asia'" _
+                        )
+    expected = "False"
+    Assert.AreEqual expected, actual
+
+TestExit:
+    Exit Sub
+TestFail:
+    Assert.Fail "Test raised an error: #" & err.Number & " - " & err.Description
+    Resume TestExit
+End Sub
+

src/Tests/TestRunner.bas

@@ -47,7 +47,7 @@ Option Explicit
 ' Argument      =     (List | Variable | Operand)
 ' List          =     "{" ["{"] SubExpr [{";" SubExpr}] ["}"] "}"
 ' Unary         =     "-" | "+" | ~
-' Operand       =     ({Digit} ["."] [{Digit}] ["E"("-" | "+"){Digit}] | (True | False))
+' Operand       =     ({Digit} ["."] [{Digit}] ["E"("-" | "+"){Digit}] | (True | False) | "'"Alphabet"'")
 ' Variable      =     Alphabet [{Decimal}] [{(Digit | Alphabet)}]
 ' Alphabet      =     "A-Z" | "a-z"
 ' Decimal       =     "."