Add mixed-case check and case converters

Introduce is_mixed_case (core) and four dedicated case converters (camel_to_snake, pascal_to_snake, snake_to_camel, snake_to_pascal) exposed from src/str.gleam and implemented in internal modules. Improve words to normalize additional Unicode whitespace characters and optimize repeat_str by switching to gleam/string_tree for better performance on large repetitions. Extend transliteration table with common symbol mappings (€, £, ¥, ©, ®, ™, …). Add tests for the new converters, update README and CHANGELOG, and bump package version to 2.1.0.

Author: lupodevelop

CHANGELOG.md

@@ -2,6 +2,20 @@
 
 All notable changes to this project are documented in this file.
 
+## [2.1.0] - 2026-03-31
+
+### Added
+
+- `is_mixed_case`: validation function to check if a string contains both uppercase and lowercase characters.
+- Dedicated case converters: `camel_to_snake`, `pascal_to_snake`, `snake_to_camel`, `snake_to_pascal` that don't aggressively strip non-alphanumeric characters.
+
+### Changed
+
+- Enhanced `words` to handle additional Unicode whitespace characters (non-breaking space, en-space, em-space, thin space, zero-width space, ideographic space).
+- Optimized string concatenation in `repeat_str` by replacing basic concatenation with `gleam/string_tree` for better performance on large string repetitions.
+
+---
+
 ## [2.0.1] - 2026-02-28
 
 ### Fixed

README.md

@@ -91,6 +91,7 @@ pub fn main() {
 | `is_uppercase(text)` | `"HELLO123"` | `True` |
 | `is_lowercase(text)` | `"hello_world"` | `True` |
 | `is_title_case(text)` | `"Hello World"` | `True` |
+| `is_mixed_case(text)` | `"helloWorld"` | `True` |
 
 ### ✂️ Grapheme Extraction
 
@@ -239,6 +240,10 @@ str.to_camel_case("hello world")    // → "helloWorld"
 str.to_pascal_case("hello world")   // → "HelloWorld"
 str.to_kebab_case("Hello World")    // → "hello-world"
 str.to_title_case("hello world")    // → "Hello World"
+str.camel_to_snake("camelCase")     // → "camel_case"
+str.snake_to_camel("snake_case")    // → "snakeCase"
+str.pascal_to_snake("PascalCase")   // → "pascal_case"
+str.snake_to_pascal("snake_case")   // → "SnakeCase"
 ```
 
 ### ASCII Folding (Deburr)

gleam.toml

@@ -1,5 +1,5 @@
 name = "str"
-version = "2.0.1"
+version = "2.1.0"
 
 # Project metadata (fill or replace placeholders before publishing)
 description = "Unicode-aware string utilities for Gleam: grapheme-safe operations, pragmatic ASCII transliteration, and slug generation."

src/str.gleam

@@ -430,6 +430,11 @@ pub fn is_lowercase(text: String) -> Bool {
   core.is_lowercase(text)
 }
 
+/// Checks if text contains both uppercase and lowercase characters.
+pub fn is_mixed_case(text: String) -> Bool {
+  core.is_mixed_case(text)
+}
+
 /// Checks if text is in Title Case format.
 pub fn is_title_case(text: String) -> Bool {
   core.is_title_case(text)
@@ -787,6 +792,26 @@ pub fn to_title_case(text: String) -> String {
   extra.to_title_case(text)
 }
 
+/// Converts camelCase or PascalCase to snake_case.
+pub fn camel_to_snake(text: String) -> String {
+  extra.camel_to_snake(text)
+}
+
+/// Alias for camel_to_snake.
+pub fn pascal_to_snake(text: String) -> String {
+  extra.pascal_to_snake(text)
+}
+
+/// Converts snake_case to camelCase.
+pub fn snake_to_camel(text: String) -> String {
+  extra.snake_to_camel(text)
+}
+
+/// Converts snake_case to PascalCase.
+pub fn snake_to_pascal(text: String) -> String {
+  extra.snake_to_pascal(text)
+}
+
 // ============================================================================
 // GRAPHEME TOKENIZATION (from str/tokenize)
 // ============================================================================

src/str/internal/core.gleam

@@ -13,6 +13,7 @@ import gleam/dict
 import gleam/int
 import gleam/list
 import gleam/string
+import gleam/string_tree
 import houdini
 import odysseus
 import str/config
@@ -154,6 +155,12 @@ pub fn words(text: String) -> List(String) {
     |> string.replace("\n", " ")
     |> string.replace("\r", " ")
     |> string.replace("\t", " ")
+    |> string.replace("\u{00A0}", " ")
+    |> string.replace("\u{2002}", " ")
+    |> string.replace("\u{2003}", " ")
+    |> string.replace("\u{2009}", " ")
+    |> string.replace("\u{200B}", " ")
+    |> string.replace("\u{3000}", " ")
 
   normalized
   |> string.split(" ")
@@ -176,13 +183,16 @@ pub fn is_blank(text: String) -> Bool {
 ///
 /// Internal helper for padding operations. Returns empty string if n <= 0.
 fn repeat_str(s: String, n: Int) -> String {
-  repeat_str_loop(s, n, "")
+  case n <= 0 {
+    True -> ""
+    False -> repeat_str_loop(s, n, string_tree.new()) |> string_tree.to_string
+  }
 }
 
-fn repeat_str_loop(s: String, n: Int, acc: String) -> String {
+fn repeat_str_loop(s: String, n: Int, acc: string_tree.StringTree) -> string_tree.StringTree {
   case n <= 0 {
     True -> acc
-    False -> repeat_str_loop(s, n - 1, acc <> s)
+    False -> repeat_str_loop(s, n - 1, string_tree.append(acc, s))
   }
 }
 
@@ -1646,6 +1656,24 @@ pub fn is_lowercase(text: String) -> Bool {
   }
 }
 
+/// Checks if text contains both uppercase and lowercase characters.
+/// Non-cased characters are ignored.
+/// Returns False for empty strings or strings with no cased characters.
+///
+///   is_mixed_case("Hello") -> True
+///   is_mixed_case("hello") -> False
+///   is_mixed_case("HELLO") -> False
+///   is_mixed_case("Hello123") -> True
+///   is_mixed_case("123") -> False
+///   is_mixed_case("") -> False
+///
+pub fn is_mixed_case(text: String) -> Bool {
+  let chars = string.to_graphemes(text)
+  let has_upper = list.any(chars, is_grapheme_uppercase)
+  let has_lower = list.any(chars, is_grapheme_lowercase)
+  has_upper && has_lower
+}
+
 /// Checks if text is in Title Case (first letter of each word is uppercase).
 /// Non-alphabetic characters are ignored. Empty strings return False.
 ///

src/str/internal/extra.gleam

@@ -394,6 +394,100 @@ pub fn to_title_case(s: String) -> String {
     })
   string.join(capitalized, " ")
 }
+
+// ----------------------------------------------------------------------------
+// Dedicated, Non-Destructive Case Converters
+// ----------------------------------------------------------------------------
+
+fn is_upper_char(g: String) -> Bool {
+  case string.to_utf_codepoints(g) {
+    [cp] -> {
+      let code = string.utf_codepoint_to_int(cp)
+      code >= 0x41 && code <= 0x5A
+    }
+    _ -> False
+  }
+}
+
+fn is_lower_char(g: String) -> Bool {
+  case string.to_utf_codepoints(g) {
+    [cp] -> {
+      let code = string.utf_codepoint_to_int(cp)
+      code >= 0x61 && code <= 0x7A
+    }
+    _ -> False
+  }
+}
+
+fn camel_to_snake_loop(chars: List(String), acc: String, prev_char: String) -> String {
+  case chars {
+    [] -> acc
+    [c, ..rest] -> {
+      let c_is_upper = is_upper_char(c)
+      let prev_is_lower = is_lower_char(prev_char)
+      let next_is_lower = case rest {
+        [n, ..] -> is_lower_char(n)
+        [] -> False
+      }
+      
+      let insert_underscore = {prev_is_lower && c_is_upper} || {is_upper_char(prev_char) && c_is_upper && next_is_lower}
+      
+      let new_acc = case insert_underscore && acc != "" && !string.ends_with(acc, "_") {
+        True -> acc <> "_" <> string.lowercase(c)
+        False -> acc <> string.lowercase(c)
+      }
+      camel_to_snake_loop(rest, new_acc, c)
+    }
+  }
+}
+
+/// Converts camelCase or PascalCase to snake_case without aggressively stripping characters.
+///
+///   camel_to_snake("camelCase") -> "camel_case"
+///   camel_to_snake("XMLHttpRequest") -> "xml_http_request"
+///
+pub fn camel_to_snake(s: String) -> String {
+  camel_to_snake_loop(string.to_graphemes(s), "", "")
+}
+
+/// Alias for camel_to_snake.
+pub fn pascal_to_snake(s: String) -> String {
+  camel_to_snake(s)
+}
+
+/// Converts snake_case to camelCase without aggressively stripping characters.
+///
+///   snake_to_camel("snake_case_name") -> "snakeCaseName"
+///
+pub fn snake_to_camel(s: String) -> String {
+  let parts = string.split(s, "_")
+  case parts {
+    [] -> ""
+    [first, ..rest] -> {
+      let camel_rest = list.fold(rest, "", fn(acc, part) {
+        case string.is_empty(part) {
+          True -> acc
+          False -> acc <> string.uppercase(string.slice(part, 0, 1)) <> string.slice(part, 1, string.length(part) - 1)
+        }
+      })
+      string.lowercase(first) <> camel_rest
+    }
+  }
+}
+
+/// Converts snake_case to PascalCase without aggressively stripping characters.
+///
+///   snake_to_pascal("snake_case_name") -> "SnakeCaseName"
+///
+pub fn snake_to_pascal(s: String) -> String {
+  let parts = string.split(s, "_")
+  list.fold(parts, "", fn(acc, part) {
+    case string.is_empty(part) {
+      True -> acc
+      False -> acc <> string.uppercase(string.slice(part, 0, 1)) <> string.slice(part, 1, string.length(part) - 1)
+    }
+  })
+}
 // Note: normalizer helpers (NFC/NFD/NFKC/NFKD) are intentionally not
 // exported by the `str` library to avoid introducing an OTP dependency.
 // If you need to use OTP normalization, define a small helper in your

src/str/internal/translit.gleam

@@ -157,6 +157,14 @@ pub fn replacements() -> List(#(String, String)) {
     // Czech/Slovak extras
     #("Ŕ", "R"),
     #("ŕ", "r"),
+    // Common Symbols
+    #("€", "EUR"),
+    #("£", "GBP"),
+    #("¥", "JPY"),
+    #("©", "(c)"),
+    #("®", "(r)"),
+    #("™", "tm"),
+    #("…", "..."),
   ]
 }
 

test/str_new_converters_test.gleam

@@ -0,0 +1,35 @@
+import gleeunit/should
+import str
+
+pub fn is_mixed_case_test() {
+  str.is_mixed_case("Hello") |> should.be_true
+  str.is_mixed_case("hello") |> should.be_false
+  str.is_mixed_case("HELLO") |> should.be_false
+  str.is_mixed_case("Hello123") |> should.be_true
+  str.is_mixed_case("123") |> should.be_false
+  str.is_mixed_case("") |> should.be_false
+}
+
+pub fn camel_to_snake_test() {
+  str.camel_to_snake("camelCase") |> should.equal("camel_case")
+  str.camel_to_snake("XMLHttpRequest") |> should.equal("xml_http_request")
+  str.camel_to_snake("simple") |> should.equal("simple")
+  str.camel_to_snake("Already_Snake") |> should.equal("already_snake")
+}
+
+pub fn pascal_to_snake_test() {
+  str.pascal_to_snake("PascalCase") |> should.equal("pascal_case")
+  str.pascal_to_snake("XMLHttpRequest") |> should.equal("xml_http_request")
+}
+
+pub fn snake_to_camel_test() {
+  str.snake_to_camel("snake_case_name") |> should.equal("snakeCaseName")
+  str.snake_to_camel("simple") |> should.equal("simple")
+  // Testing numbers and acroynms
+  str.snake_to_camel("xml_http_request") |> should.equal("xmlHttpRequest")
+}
+
+pub fn snake_to_pascal_test() {
+  str.snake_to_pascal("snake_case_name") |> should.equal("SnakeCaseName")
+  str.snake_to_pascal("simple") |> should.equal("Simple")
+}