started writing lexer after making string lib

string/docs/classify/is_alpha.md

@@ -0,0 +1,24 @@
+# string_IsAlpha
+Returns true if the given `string` is only the letters a-Z.
+
+## Arguments
+- str (string): the string to check.
+
+## Returns
+isAlpha (bool): returns `true` if `string` is only the letters a-Z, otherwise `false`.
+
+## Example
+### Ground
+```python
+call !string_IsAlpha "abcABC" &isAlpha
+println $isAlpha # true
+
+call !string_IsAlpha "123" &isAlpha
+println $isAlpha # false
+
+call !string_IsAlpha "abc_$@" &isAlpha
+println $isAlpha # false
+
+call !string_IsAlpha "aAbBcCdDeEfF" &isAlpha
+println $isAlpha # true
+```