use string functions to mod

Author: nafasebra

src/builtin_function/mod.rs

@@ -80,6 +80,10 @@ pub fn function_match(function_name: &str) -> Option<BuiltinFunction> {
         "length" | "len" => Some(strings::length::length),
         "contains" | "has" => Some(strings::contains::contains),
         "slice" | "substring" => Some(strings::slice::slice),
+        "charat" => Some(strings::char_at::char_at),
+        "toupper" | "uppercase" => Some(strings::to_upper::to_upper),
+        "tolower" | "lowercase" => Some(strings::to_lower::to_lower),
+        "trim" => Some(strings::trim::trim),
         "insert" | "push" => Some(list::insert::insert),
         "get" | "at" => Some(list::get::get),
         "pop" => Some(list::pop::pop),

src/builtin_function/strings/mod.rs

@@ -1,5 +1,9 @@
+pub mod char_at;
 pub mod contact;
 pub mod contains;
 pub mod length;
 pub mod repeat;
 pub mod slice;
+pub mod to_lower;
+pub mod to_upper;
+pub mod trim;