spec: format — CL-style string formatting (~a ~s ~d ~x ~o ~b ~f ~% ~& ~~ ~t)

28 tests, passes on both JS and OCaml.
- spec/stdlib.sx: pure SX format function
- spec/primitives.sx: format primitive declaration
- lib/r7rs.sx: fix number->string to support optional radix arg
- hosts/ocaml: add format-decimal primitive, load stdlib.sx in test runner
- hosts/javascript: load stdlib.sx in test runner

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

spec/tests/test-format.sx

@@ -0,0 +1,90 @@
+;; ==========================================================================
+;; test-format.sx — Tests for CL-style format function
+;; ==========================================================================
+
+;; --------------------------------------------------------------------------
+;; basic directives
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "format:basic"
+  (deftest "format returns string" (assert (string? (format "hello"))))
+  (deftest
+    "format no directives"
+    (assert= (format "hello world") "hello world"))
+  (deftest "format empty template" (assert= (format "") ""))
+  (deftest "~a display string" (assert= (format "~a" "hello") "hello"))
+  (deftest "~a display number" (assert= (format "~a" 42) "42"))
+  (deftest "~a display nil" (assert= (format "~a" nil) "()"))
+  (deftest
+    "~s write string (with quotes)"
+    (assert= (format "~s" "hi") "\"hi\""))
+  (deftest "~s write number" (assert= (format "~s" 42) "42"))
+  (deftest
+    "multiple args"
+    (assert= (format "~a and ~a" "foo" "bar") "foo and bar")))
+
+;; --------------------------------------------------------------------------
+;; numeric directives
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "format:numeric"
+  (deftest "~d decimal" (assert= (format "~d" 255) "255"))
+  (deftest "~x hex" (assert= (format "~x" 255) "ff"))
+  (deftest "~o octal" (assert= (format "~o" 8) "10"))
+  (deftest "~b binary" (assert= (format "~b" 10) "1010"))
+  (deftest "~d zero" (assert= (format "~d" 0) "0"))
+  (deftest
+    "~x uppercase digits"
+    (assert= (format "value: ~x" 16) "value: 10")))
+
+;; --------------------------------------------------------------------------
+;; float directives
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "format:float"
+  (deftest "~f fixed point" (assert= (format "~f" 3.14) "3.140000"))
+  (deftest "~f zero" (assert= (format "~f" 0) "0.000000")))
+
+;; --------------------------------------------------------------------------
+;; control directives
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "format:control"
+  (deftest "~% newline" (assert= (format "a~%b") "a\nb"))
+  (deftest "~~ literal tilde" (assert= (format "100~~") "100~"))
+  (deftest "~t tab" (assert= (format "a~tb") "a\tb"))
+  (deftest "~& fresh line at start" (assert= (format "~&hello") "\nhello"))
+  (deftest
+    "~& no newline if already at newline"
+    (assert= (format "line~%~&next") "line\nnext")))
+
+;; --------------------------------------------------------------------------
+;; mixed / compound
+;; --------------------------------------------------------------------------
+
+(defsuite
+  "format:compound"
+  (deftest
+    "name and age"
+    (assert=
+      (format "Hello ~a, age ~d" "Alice" 30)
+      "Hello Alice, age 30"))
+  (deftest
+    "hex dump style"
+    (assert=
+      (format "~d = 0x~x = 0b~b" 10 10 10)
+      "10 = 0xa = 0b1010"))
+  (deftest "multiple newlines" (assert= (format "~%~%") "\n\n"))
+  (deftest "text with no args" (assert= (format "status: ok") "status: ok"))
+  (deftest
+    "tilde at end (unknown directive)"
+    (assert (string? (format "test~"))))
+  (deftest
+    "nested strings in ~a"
+    (assert=
+      (format "got: ~a" (list 1 2 3))
+      "got: (1 2 3)")))