From a66038a42761b31c2d883d621bae7a1c6ed03910 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Fri, 7 Dec 2018 11:03:53 -0700
Subject: [PATCH] io: shortcut for common `format` patterns

---
 racket/src/io/demo.rkt        | 12 +++++++++
 racket/src/io/format/main.rkt | 46 ++++++++++++++++++++++++++++-------
 2 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/racket/src/io/demo.rkt b/racket/src/io/demo.rkt
index f08456bf3e..f8563bc157 100644
--- a/racket/src/io/demo.rkt
+++ b/racket/src/io/demo.rkt
@@ -91,6 +91,18 @@
   #:property prop:custom-write (lambda (v o mode)
                                  (fprintf o "<~a>" (animal-name v))))
 
+(test "apple" (format "~a" 'apple))
+(test "apple" (format "~a" "apple"))
+(test "apple" (format "~a" #"apple"))
+(test "#:apple" (format "~a" '#:apple))
+(test "17.5" (format "~a" 17.5))
+
+(test "apple" (format "~s" 'apple))
+(test "\"apple\"" (format "~s" "apple"))
+(test "#\"apple\"" (format "~s" #"apple"))
+(test "#:apple" (format "~s" '#:apple))
+(test "17.5" (format "~s" 17.5))
+
 (test "1\n\rx0!\"hi\"" (format "1~%~  \n  \rx~ ~o~c~s" 0 #\! "hi"))
 
 (test "*(1 2 3 apple\t\u0001 end <spot> file 1\"2\"3 #hash((a . 1) (b . 2)))*"
diff --git a/racket/src/io/format/main.rkt b/racket/src/io/format/main.rkt
index def8484c2c..2d71fff43a 100644
--- a/racket/src/io/format/main.rkt
+++ b/racket/src/io/format/main.rkt
@@ -3,18 +3,13 @@
          "../port/parameter.rkt"
          "../port/output-port.rkt"
          "../port/string-port.rkt"
+         "../string/convert.rkt"
          "printf.rkt")
 
-(provide format
-         fprintf
+(provide fprintf
          printf
-         eprintf)
-
-(define/who (format fmt . args)
-  (check who string? fmt)
-  (define o (open-output-string))
-  (do-printf 'printf o fmt args)
-  (get-output-string o))
+         eprintf
+         format)
 
 (define/who (fprintf o fmt . args)
   (check who output-port? o)
@@ -28,3 +23,36 @@
 (define/who (eprintf fmt . args)
   (check who string? fmt)
   (do-printf who (current-error-port) fmt args))
+
+;; ----------------------------------------
+
+(define (general-format fmt args)
+  (check 'format string? fmt)
+  (define o (open-output-string))
+  (do-printf 'format o fmt args)
+  (get-output-string o))
+
+(define (simple-format a)
+  (cond
+    [(boolean? a) (string-copy (if a "#t" "#f"))]
+    [(number? a) (number->string a)]
+    [(symbol? a) (symbol->string a)]
+    [(keyword? a) (string-append "#:" (keyword->string a))]
+    [else #f]))
+
+(define format
+  (case-lambda
+    [(fmt a)
+     (cond
+       [(or (equal? fmt "~a") (equal? fmt "~A"))
+        (or (simple-format a)
+            (cond
+              [(bytes? a) (bytes->string/utf-8 a #\?)]
+              [(string? a) (string-copy a)]
+              [else (general-format fmt (list a))]))]
+       [(or (equal? fmt "~s") (equal? fmt "~S"))
+        (or (simple-format a)
+            (general-format fmt (list a)))]
+       [else (general-format fmt (list a))])]
+    [(fmt . args)
+     (general-format fmt args)]))