diff --git a/beautiful-racket-lib/br/indent.rkt b/beautiful-racket-lib/br/indent.rkt
index 373acc9..54ae9a4 100644
--- a/beautiful-racket-lib/br/indent.rkt
+++ b/beautiful-racket-lib/br/indent.rkt
@@ -2,7 +2,8 @@
 (require racket/class
          racket/gui/base
          racket/list
-         racket/string)
+         racket/string
+         racket/contract)
 (provide (all-defined-out))
 
 (module+ test
@@ -14,7 +15,8 @@
 
 (define indent-width 2)
 
-(define (char text pos)
+(define/contract (char text pos)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . char?)
   (and pos (send text get-character pos)))
 
 (module+ test
@@ -24,7 +26,8 @@
   (check-equal? (char t 10) #\m)
   (check-equal? (char t 11) #\nul))
 
-(define (line text pos)
+(define/contract (line text pos)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . exact-nonnegative-integer?)
   (send text position-line pos))
 
 (module+ test
@@ -34,7 +37,8 @@
   (check-equal? (line t 10) 2)
   (check-equal? (line t 11) 2))
 
-(define (line-chars text line)
+(define/contract (line-chars text line)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . (or/c (listof char?) #f))
   (and
    (valid-line? text line)
    (for/list ([pos (in-range (line-start text line) (add1 (line-end text line)))])
@@ -47,7 +51,8 @@
   (check-equal? (line-chars t 3) #f))
 
 
-(define (previous-line text pos)
+(define/contract (previous-line text pos)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . (or/c exact-nonnegative-integer? #f))
   (define this-line (line text pos))
   (and (this-line . > . 0) (sub1 this-line)))
 
@@ -58,7 +63,8 @@
   (check-equal? (previous-line t 10) 1)
   (check-equal? (previous-line t 11) 1))
 
-(define (next-line text pos)
+(define/contract (next-line text pos)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . (or/c exact-nonnegative-integer? #f))
   (define last (send text last-line))
   (define this-line (line text pos))
   (and (this-line . < . last) (add1 this-line)))
@@ -70,10 +76,12 @@
   (check-equal? (next-line t 10) #f)
   (check-equal? (next-line t 11) #f))
 
-(define (valid-line? text line)
+(define/contract (valid-line? text line)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . boolean?)
   (and line (<= 0 line (send text last-line))))
 
-(define (line-start text line)
+(define/contract (line-start text line)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . (or/c exact-nonnegative-integer? #f))
   (and (valid-line? text line)
        (send text line-start-position line)))
 
@@ -83,7 +91,8 @@
   (check-equal? (line-start t 2) 8)
   (check-equal? (line-start t 3) #f))
   
-(define (line-end text line)
+(define/contract (line-end text line)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . (or/c exact-nonnegative-integer? #f))
   (and (valid-line? text line)
        (send text line-end-position line)))
 
@@ -100,7 +109,8 @@
                #:when (not (char-blank? c)))
               pos))
 
-(define (line-start-visible text line)
+(define/contract (line-start-visible text line)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . (or/c exact-nonnegative-integer? #f))
   (define start (line-start text line))
   (define end (line-end text line))
   (and start end (first-visible-char-pos text start end)))
@@ -111,7 +121,8 @@
   (check-equal? (line-start-visible t 2) 10)
   (check-equal? (line-start-visible t 3) #f))
 
-(define (line-end-visible text line)
+(define/contract (line-end-visible text line)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . (or/c exact-nonnegative-integer? #f))
   (define start+1 (line-end text line)) ; start before newline
   (define end+1 (line-start text line))
   (and start+1 end+1 (first-visible-char-pos text (sub1 start+1) (sub1 end+1))))
@@ -122,7 +133,8 @@
   (check-equal? (line-end-visible t 2) 10)
   (check-equal? (line-end-visible t 3) #f))
 
-(define (line-indent text line)
+(define/contract (line-indent text line)
+  ((is-a?/c text%) exact-nonnegative-integer? . -> . (or/c exact-nonnegative-integer? #f))
   (and (valid-line? text line)
        (let ([lsv (line-start-visible text line)])
          (and lsv ; could be #f
@@ -152,9 +164,10 @@
   (send t insert-port (open-input-string str))
   t)
 
-(define space-char? (λ(x) (x . char=? . #\space)))
+(define (space-char? x) (char=? x #\space))
 
-(define (test-indenter indenter t-or-str)
+(define/contract (apply-indenter indenter t-or-str)
+  (procedure? (or/c (is-a?/c text%) string?) . -> . string?)
   (define t (if (string? t-or-str) (str->text t-or-str) t-or-str))
   (define indented-t
     (for/fold ([t-acc t])
@@ -171,9 +184,10 @@
       t-acc))
   (send indented-t get-text))
 
-(define (str->indents str)
+(define/contract (string-indents str)
+  (string? . -> . (listof exact-nonnegative-integer?))
   (for/list ([line (in-list (string-split str "\n"))])
             (length (takef (string->list line) space-char?))))
 
 (module+ test
-  (check-equal? (str->indents t-str) '(0 1 2)))
\ No newline at end of file
+  (check-equal? (string-indents t-str) '(0 1 2)))
\ No newline at end of file
diff --git a/beautiful-racket/br/demo/jsonic-2/indenter.rkt b/beautiful-racket/br/demo/jsonic-2/indenter.rkt
index f64542d..38b75ed 100644
--- a/beautiful-racket/br/demo/jsonic-2/indenter.rkt
+++ b/beautiful-racket/br/demo/jsonic-2/indenter.rkt
@@ -1,28 +1,25 @@
-#lang at-exp br
+#lang br
 (require br/indent)
 (provide indent-jsonic)
 
 (define indent-width 2)
 
-(define (left-bracket? c)
-   (and c (or (char=? c #\{) (char=? c #\[))))
+(define (left-bracket? c) (member c '(#\{ #\[)))
+(define (right-bracket? c) (member c '(#\} #\])))
 
-(define (right-bracket? c)
-   (and c (or (char=? c #\}) (char=? c #\]))))
-
-(define (indent-jsonic tb [this-pos 0])
-  (define this-line (line tb this-pos))
-  (define prev-line (previous-line tb this-pos))
-  (define prev-indent (or (line-indent tb prev-line) 0))
+;; if this line begins with } or ], outdent.
+;; if last line begins with { or [, indent.
+;; otherwise use previous indent
+(define (indent-jsonic textbox [pos 0])
+  (define this-line (line textbox pos))
+  (define prev-line (previous-line textbox pos))
+  (define prev-indent (or (line-indent textbox prev-line) 0))
   (define this-indent
     (cond
-      ;; if this line begins with }, outdent.
-      [(right-bracket? (char tb (line-start-visible tb this-line)))
-       (- prev-indent indent-width)]
-      ;; if last line begins with {, indent.
-      [(left-bracket? (char tb (line-start-visible tb prev-line)))
+      [(left-bracket? (char textbox (line-start-visible textbox prev-line)))
        (+ prev-indent indent-width)]
-      ;; otherwise use previous indent
+      [(right-bracket? (char textbox (line-start-visible textbox this-line)))
+       (- prev-indent indent-width)]
       [else prev-indent]))
   (and (exact-positive-integer? this-indent) this-indent))
 
@@ -40,5 +37,5 @@
 }
 here
     )
-  (check-equal? (str->indents (test-indenter indent-jsonic test-str))
+  (check-equal? (string-indents (apply-indenter indent-jsonic test-str))
                 (map (λ(x) (* x indent-width)) '(0 0 1 1 2 2 1 1 0))))