ocaml: phase 6 Char predicates (+7 tests, 461 total)

Char.is_digit / is_alpha / is_alnum / is_whitespace / is_upper /
is_lower / is_space — all written in OCaml using Char.code + ASCII
range checks.

lib/ocaml/runtime.sx

@@ -377,6 +377,16 @@
      let chr n = _char_chr n
      let lowercase_ascii c = _string_lower c
      let uppercase_ascii c = _string_upper c
+     let is_digit c =
+       let n = _char_code c in n >= 48 && n <= 57
+     let is_lower c =
+       let n = _char_code c in n >= 97 && n <= 122
+     let is_upper c =
+       let n = _char_code c in n >= 65 && n <= 90
+     let is_alpha c = is_lower c || is_upper c
+     let is_alnum c = is_alpha c || is_digit c
+     let is_whitespace c =
+       c = \" \" || c = \"\\t\" || c = \"\\n\" || c = \"\\r\"
    end ;;
 
    module Int = struct