Add string comparator helpers and remove main function

Introduced by_string_with and by_normalized_string helpers for flexible string comparison, allowing custom key extraction and normalization. Also removed the unused main function and redundant io import.

Author: lupodevelop

src/cmp.gleam

@@ -1,4 +1,3 @@
-import gleam/io
 
 import gleam/int
 import gleam/option
@@ -73,6 +72,28 @@ pub fn by(key: fn(a) -> b, cmp: fn(b, b) -> order.Order) -> Comparator(a) {
   fn(x, y) { cmp(key(x), key(y)) }
 }
 
+/// Sugar for string comparators: pass a string key extractor and a string
+/// comparator (e.g. `string.compare` or `str.compare`). This helper does not
+/// import or depend on `str`; it only accepts a comparator function as an
+/// argument so the user may pass `str.compare` if they use the `str` package.
+pub fn by_string_with(
+  key: fn(a) -> String,
+  cmp: fn(String, String) -> order.Order,
+) -> Comparator(a) {
+  fn(x, y) { cmp(key(x), key(y)) }
+}
+
+/// Normalize keys with `normalize` before applying `cmp`. Useful if you want
+/// to apply folding/normalization (e.g. ASCII folding) prior to comparing.
+/// `normalize` can be any function (for example from `str/extra`).
+pub fn by_normalized_string(
+  key: fn(a) -> String,
+  normalize: fn(String) -> String,
+  cmp: fn(String, String) -> order.Order,
+) -> Comparator(a) {
+  fn(x, y) { cmp(normalize(key(x)), normalize(key(y))) }
+}
+
 /// Build a comparator for `Option(a)` given:
 /// - `none_order`: the `order.Order` to use when comparing `None` with `Some(_)`.
 ///   Use `order.Lt` for `None` < `Some`, `order.Gt` for `None` > `Some`.
@@ -210,7 +231,3 @@ fn list_compare_go(elem_cmp: fn(a, a) -> order.Order, xl: List(a), yl: List(a))
 pub fn list_compare(elem_cmp: fn(a, a) -> order.Order) -> Comparator(List(a)) {
   fn(xs, ys) { list_compare_go(elem_cmp, xs, ys) }
 }
-
-pub fn main() -> Nil {
-  io.println("Hello from cmp!")
-}