ocaml: phase 6 Filename module + Char.compare/equal/escaped (+7 tests, 569 total)

Filename module (forward-slash only, no Windows-separator detection):

  basename '/foo/bar/baz.ml'        = 'baz.ml'
  dirname  '/foo/bar/baz.ml'        = '/foo/bar'
  extension 'baz.tar.gz'            = '.gz'
  chop_extension 'hello.ml'         = 'hello'
  concat 'a' 'b'                    = 'a/b'
  is_relative 'a/b'                 = true
  current_dir_name = '.', parent_dir_name = '..', dir_sep = '/'

Char additions:

  equal a b                         = (a = b)
  compare a b                       = code(a) - code(b)
  escaped '\n'                      = '\\n'    (likewise t, r, \\, ")

lib/ocaml/runtime.sx

@@ -474,6 +474,69 @@
      let is_alnum c = is_alpha c || is_digit c
      let is_whitespace c =
        c = \" \" || c = \"\\t\" || c = \"\\n\" || c = \"\\r\"
+     let equal a b = a = b
+     let compare a b = _char_code a - _char_code b
+     let escaped c =
+       if c = \"\\n\" then \"\\\\n\"
+       else if c = \"\\t\" then \"\\\\t\"
+       else if c = \"\\r\" then \"\\\\r\"
+       else if c = \"\\\\\" then \"\\\\\\\\\"
+       else if c = \"\\\"\" then \"\\\\\\\"\"
+       else c
+   end ;;
+
+   module Filename = struct
+     (* Minimal Filename: basename / dirname / extension / concat /
+        chop_suffix.  Forward-slash only — doesn't try to detect
+        Windows-style separators. *)
+     let _last_slash s =
+       let n = _string_length s in
+       let rec aux i =
+         if i < 0 then -1
+         else if _string_get s i = \"/\" then i
+         else aux (i - 1)
+       in
+       aux (n - 1)
+
+     let basename s =
+       let i = _last_slash s in
+       if i < 0 then s
+       else _string_sub s (i + 1) (_string_length s - i - 1)
+
+     let dirname s =
+       let i = _last_slash s in
+       if i < 0 then \".\"
+       else if i = 0 then \"/\"
+       else _string_sub s 0 i
+
+     let extension s =
+       let b = basename s in
+       let n = _string_length b in
+       let rec aux i =
+         if i < 0 then \"\"
+         else if _string_get b i = \".\" then
+           _string_sub b i (n - i)
+         else aux (i - 1)
+       in
+       aux (n - 1)
+
+     let chop_extension s =
+       let ext = extension s in
+       let nx = _string_length ext in
+       if nx = 0 then s
+       else _string_sub s 0 (_string_length s - nx)
+
+     let concat a b =
+       if _string_length a = 0 then b
+       else if _string_get a (_string_length a - 1) = \"/\" then a ^ b
+       else a ^ \"/\" ^ b
+
+     let is_relative s =
+       _string_length s = 0 || _string_get s 0 <> \"/\"
+
+     let current_dir_name = \".\"
+     let parent_dir_name = \"..\"
+     let dir_sep = \"/\"
    end ;;
 
    module Int = struct