[format] add define form

test/format-fail.rkt

@@ -4,7 +4,7 @@
 ;; `format:` expressions that should fail to compile
 
 (module+ test (test-compile-error
-  #:require trivial/format
+  #:require trivial/format trivial/define
   #:exn #rx"format::|Type Checker"
   (printf: "hello ~a" "john" "doe")
   (printf: "hello ~a" "john" "doe")
@@ -12,4 +12,9 @@
   (printf: "character ~c\n" 88)
   (printf: "octl ~o\n" 1.0+2i)
   (printf: "hex ~o\n" (exact->inexact 0))
+  (let ()
+    (define: s "asdf ~a asdf")
+    (printf: s))
+  (let: ([s "asdf ~a asdf"])
+    (printf: s))
 ))

trivial/define.rkt

@@ -11,6 +11,9 @@
     trivial/private/common
     syntax/parse
     typed/racket/base)
+  (only-in trivial/private/format
+    format-define
+    format-let)
   (only-in trivial/private/math
     num-define
     num-let)
@@ -26,14 +29,16 @@
 
 (define-syntax define: (make-keyword-alias 'define
   (lambda (stx)
-    (or (num-define stx)
+    (or (format-define stx)
+        (num-define stx)
         (rx-define stx)
         (fun-define stx)
         (vec-define stx)))))
 
 (define-syntax let: (make-keyword-alias 'let
   (lambda (stx)
-    (or (fun-let stx)
+    (or (format-let stx)
+        (fun-let stx)
         (num-let stx)
         (rx-let stx)
         (vec-let stx)))))

trivial/private/format.rkt

@@ -5,6 +5,10 @@
 (provide
   format:
   printf:
+
+  (for-syntax
+    format-define
+    format-let)
 )
 
 (require
@@ -59,7 +63,7 @@
           (loop (+ i 1) acc)]))]
      [else #f]))
 
-  (define-values (_key fmt? _define _let)
+  (define-values (_key fmt? format-define format-let)
     (make-value-property 'string:format format-parser))
 
   (define-syntax-class/predicate string/format fmt?)