spec: character type (char? char->integer #\a literals + predicates)

- Add SxChar tagged object {_char, codepoint} to JS platform
- char? char->integer integer->char char-upcase char-downcase
- char=? char<? char>? char<=? char>=? comparators
- char-ci=? char-ci<? char-ci>? char-ci<=? char-ci>=? case-insensitive
- char-alphabetic? char-numeric? char-whitespace? char-upper-case? char-lower-case?
- string->list (returns chars) and list->string (accepts chars)
- #\a #\space #\newline reader syntax in spec/parser.sx
- integer->char alias in spec/evaluator.sx
- js-char-renames dict in transpiler.sx for ->-containing names
- 43 tests in spec/tests/test-chars.sx, all passing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

spec/tests/test-chars.sx

@@ -0,0 +1,185 @@
+;; Tests for character type (Phase 13)
+;; Uses (make-char n) and (char-code "x") instead of #\x literals
+;; (char literal parser syntax tested via sx-parse call)
+
+(deftest
+  "make-char produces a char"
+  (assert= true (char? (make-char 97))))
+
+(deftest "char? false for string" (assert= false (char? "a")))
+
+(deftest "char? false for number" (assert= false (char? 65)))
+
+(deftest "char? false for nil" (assert= false (char? nil)))
+
+(deftest
+  "char->integer extracts codepoint"
+  (assert= 97 (char->integer (make-char 97))))
+
+(deftest
+  "integer->char alias for make-char"
+  (assert= 65 (char->integer (integer->char 65))))
+
+(deftest
+  "char->integer round-trip"
+  (assert= 122 (char->integer (make-char 122))))
+
+(deftest
+  "char=? equal"
+  (assert= true (char=? (make-char 97) (make-char 97))))
+
+(deftest
+  "char=? unequal"
+  (assert= false (char=? (make-char 97) (make-char 98))))
+
+(deftest
+  "char<? ordering"
+  (assert= true (char<? (make-char 97) (make-char 98))))
+
+(deftest
+  "char>? ordering"
+  (assert= true (char>? (make-char 98) (make-char 97))))
+
+(deftest
+  "char<=? equal"
+  (assert= true (char<=? (make-char 65) (make-char 65))))
+
+(deftest
+  "char>=? greater"
+  (assert= true (char>=? (make-char 90) (make-char 65))))
+
+(deftest
+  "char-ci=? ignores case (a vs A)"
+  (assert= true (char-ci=? (make-char 97) (make-char 65))))
+
+(deftest
+  "char-ci<? a < b case-insensitive"
+  (assert= true (char-ci<? (make-char 97) (make-char 98))))
+
+(deftest
+  "char-ci>? b > a case-insensitive"
+  (assert= true (char-ci>? (make-char 66) (make-char 65))))
+
+(deftest
+  "char-alphabetic? true for a"
+  (assert= true (char-alphabetic? (make-char 97))))
+
+(deftest
+  "char-alphabetic? true for Z"
+  (assert= true (char-alphabetic? (make-char 90))))
+
+(deftest
+  "char-alphabetic? false for digit"
+  (assert= false (char-alphabetic? (make-char 48))))
+
+(deftest
+  "char-numeric? true for 0"
+  (assert= true (char-numeric? (make-char 48))))
+
+(deftest
+  "char-numeric? true for 9"
+  (assert= true (char-numeric? (make-char 57))))
+
+(deftest
+  "char-numeric? false for letter"
+  (assert= false (char-numeric? (make-char 65))))
+
+(deftest
+  "char-whitespace? true for space"
+  (assert= true (char-whitespace? (make-char 32))))
+
+(deftest
+  "char-whitespace? true for newline"
+  (assert= true (char-whitespace? (make-char 10))))
+
+(deftest
+  "char-whitespace? false for letter"
+  (assert= false (char-whitespace? (make-char 65))))
+
+(deftest
+  "char-upper-case? true for A"
+  (assert= true (char-upper-case? (make-char 65))))
+
+(deftest
+  "char-upper-case? false for a"
+  (assert= false (char-upper-case? (make-char 97))))
+
+(deftest
+  "char-lower-case? true for a"
+  (assert= true (char-lower-case? (make-char 97))))
+
+(deftest
+  "char-lower-case? false for A"
+  (assert= false (char-lower-case? (make-char 65))))
+
+(deftest
+  "char-upcase converts a to A"
+  (assert= 65 (char->integer (char-upcase (make-char 97)))))
+
+(deftest
+  "char-downcase converts A to a"
+  (assert=
+    97
+    (char->integer (char-downcase (make-char 65)))))
+
+(deftest
+  "char-upcase idempotent on uppercase"
+  (assert= 65 (char->integer (char-upcase (make-char 65)))))
+
+(deftest
+  "string->list returns list of chars"
+  (assert= 3 (len (string->list "abc"))))
+
+(deftest
+  "string->list element 0 is char"
+  (assert= true (char? (get (string->list "abc") 0))))
+
+(deftest
+  "string->list codepoints correct"
+  (assert= 97 (char->integer (get (string->list "abc") 0))))
+
+(deftest
+  "list->string from chars produces string"
+  (assert=
+    "abc"
+    (list->string
+      (list
+        (make-char 97)
+        (make-char 98)
+        (make-char 99)))))
+
+(deftest
+  "string->list list->string round-trip"
+  (let ((s "hello")) (assert= s (list->string (string->list s)))))
+
+(deftest
+  "char literal parsed via sx-parse"
+  (let
+    ((ast (sx-parse "#\\a")))
+    (assert= true (char? (get ast 0)))))
+
+(deftest
+  "char literal codepoint via sx-parse"
+  (let
+    ((ast (sx-parse "#\\a")))
+    (assert= 97 (char->integer (get ast 0)))))
+
+(deftest
+  "named char space via sx-parse"
+  (let
+    ((ast (sx-parse "#\\space")))
+    (assert= 32 (char->integer (get ast 0)))))
+
+(deftest
+  "named char newline via sx-parse"
+  (let
+    ((ast (sx-parse "#\\newline")))
+    (assert= 10 (char->integer (get ast 0)))))
+
+(deftest
+  "char-ci<=? equal case-insensitive"
+  (assert= true (char-ci<=? (make-char 65) (make-char 97))))
+
+(deftest
+  "char-ci>=? equal case-insensitive"
+  (assert= true (char-ci>=? (make-char 97) (make-char 65))))