Add print-value-columns parameter.

pkgs/racket-doc/scribblings/reference/write.scrbl

@@ -272,6 +272,16 @@ A @tech{parameter} that controls printing of @tech{syntax objects}. Up to
 object within @litchar{#<syntax}...@litchar{>} (after the
 @tech{syntax object}'s source location, if any).}
 
+@defparam[print-value-columns columns (or/c +inf.0 (and/c exact-integer? (>/c 5)))]{
+
+A @tech{parameter} that contains a recommendation for the number of
+columns that should be used for printing values via @racket[print].
+May or may not be respected by @racket[print] - the current default
+handler for @racket[print] does not.  It is expected that REPLs that use
+some form of pretty-printing for values respect this parameter.
+
+@history[#:added "8.0.0.13"]
+}
 
 @defparam*[current-write-relative-directory path 
                                             (or/c (and/c path-string? complete-path?) 

pkgs/racket-test/tests/racket/print-value-columns.rkt

@@ -0,0 +1,11 @@
+#lang racket/base
+(require rackunit)
+
+(check-equal? (parameterize ((print-value-columns 10))
+                (print-value-columns))
+              10)
+(check-equal? (parameterize ((print-value-columns +inf.0))
+                (print-value-columns))
+              +inf.0)
+(check-exn exn:fail? (lambda () (print-value-columns -5)))
+(check-exn exn:fail? (lambda () (print-value-columns 'wrong)))

racket/collects/racket/private/base.rkt

@@ -12,6 +12,7 @@
              "cert.rkt"
              "submodule.rkt"
              "generic-interfaces.rkt"
+             "print-value-columns.rkt"
              "kw-syntax-binding.rkt" ; shadows `syntax-binding-set-extend`
              "kw-syntax-serialize.rkt" ; shadows `syntax-serialize` and `syntax-deserialize
              (for-syntax "stxcase-scheme.rkt"))
@@ -40,6 +41,7 @@
              (all-from "cert.rkt")
              (all-from "submodule.rkt")
              (all-from "generic-interfaces.rkt")
+             (all-from "print-value-columns.rkt")
              (all-from "kw-syntax-binding.rkt")
              (all-from "kw-syntax-serialize.rkt")
              (for-syntax syntax-rules syntax-id-rules ... _)

racket/collects/racket/private/print-value-columns.rkt

@@ -0,0 +1,14 @@
+(module print-value-columns "pre-base.rkt"
+  (#%provide print-value-columns)
+  
+  (define print-value-columns
+    (make-parameter +inf.0
+                    (lambda (c)
+                      (if (or  (eqv? c +inf.0)
+                               (and (exact-integer? c)
+                                    ; somewhat arbitrary value, enough for "(list"
+                                    (> c 5)))
+                          c
+                          (raise-argument-error 'print-value-columns "(or/c +inf.0 (and/c exact-integer? (>/c 5)))" c)))
+                    'print-value-columns)))
+