racket' -> racket/base' switches in htdp' and 2htdp'.

All of these look safe.  Also, see comment in `2htdp/batch-io' about the
splitting thing (which should probably be revised with the extensions to
`racket/string').

collects/2htdp/batch-io.rkt

@@ -1,7 +1,12 @@
-#lang racket
+#lang racket/base
 
-(require (for-syntax syntax/parse)
-         srfi/13 htdp/error
+(require racket/function
+         racket/file
+         racket/string
+         racket/local
+         (for-syntax racket/base
+                     syntax/parse)
+         htdp/error
          (rename-in lang/prim (first-order->higher-order f2h))
          "private/csv/csv.rkt")
 
@@ -163,10 +168,13 @@
 ;; split : String [Regexp] -> [Listof String]
 ;; splits a string into a list of substrings using the given delimiter
 ;; (white space by default)
+;;ELI: This shouldn't be needed now, it can use `string-split' as is
+;; (also, the trimming doesn't make sense if the pattern is not a
+;; space--?)
 (define (split str [ptn #rx"[ ]+"])
-  (regexp-split ptn (string-trim-both str)))
+  (regexp-split ptn (string-trim str)))
 
 ;; split-lines : String -> Listof[String]
 ;; splits a string with newlines into a list of lines
 (define (split-lines str)
-  (map string-trim-both (split str "\r*\n")))
+  (map string-trim (split str "\r*\n")))

collects/2htdp/private/check-aux.rkt

@@ -1,6 +1,10 @@
-#lang racket
+#lang racket/base
 
-(require htdp/error)
+(require racket/class
+         racket/list
+         racket/bool
+         racket/match
+         htdp/error)
 
 (provide (all-defined-out))
 

collects/2htdp/private/clauses-spec-and-process.rkt

@@ -1,4 +1,4 @@
-#lang racket
+#lang racket/base
 
 ;; ---------------------------------------------------------------------------------------------------
 ;; provides functions for specifying the shape of big-bang and universe clauses:
@@ -12,9 +12,14 @@
          ->args
          contains-clause?)
 
-(require 
- (for-syntax syntax/parse)
- (for-template "clauses-spec-aux.rkt" racket (rename-in lang/prim (first-order->higher-order f2h))))
+(require racket/function
+         racket/list
+         racket/bool
+         (only-in racket/unit except) ; used only as a keyword...?
+         (for-syntax racket/base syntax/parse)
+         (for-template "clauses-spec-aux.rkt"
+                       racket
+                       (rename-in lang/prim (first-order->higher-order f2h))))
 
 ;; ---------------------------------------------------------------------------------------------------
 ;; specifying the shape of clauses 

collects/2htdp/private/define-keywords.rkt

@@ -1,4 +1,4 @@
-#lang racket
+#lang racket/base
 
 ;; ---------------------------------------------------------------------------------------------------
 ;; provide a mechanism for defining the shape of big-bang and universe clauses 
@@ -6,7 +6,8 @@
 
 (provide define-keywords DEFAULT)
 
-(require (for-syntax syntax/parse))
+(require racket/class
+         (for-syntax racket/base syntax/parse))
 
 (define-syntax (DEFAULT stx)
   (raise-syntax-error 'DEFAULT "used out of context" stx))

collects/2htdp/private/launch-many-worlds.rkt

@@ -1,6 +1,7 @@
-#lang racket 
+#lang racket/base
 
-(require mred/mred mzlib/etc htdp/error)
+(require racket/list racket/function racket/gui
+         mzlib/etc htdp/error)
 
 (provide
  ;; (launch-many-worlds e1 ... e2)

collects/2htdp/private/utilities.rkt

@@ -1,4 +1,6 @@
-#lang racket
+#lang racket/base
+
+(require racket/contract)
 
 (provide/contract
  ;; like the unix debugging facility

collects/htdp/dir.rkt

@@ -1,4 +1,4 @@
-#lang racket
+#lang racket/base
 
 (provide
  ;; map the directory tree at the given path into a data representation according to model 3 of