1 files changed, 114 insertions, 0 deletions
diff --git a/main.rkt b/main.rkt
new file mode 100644
index 0000000..8bf8222
--- /dev/null
+++ b/main.rkt
@@ -0,0 +1,114 @@
+#lang racket
+(require pict)
+
+(define CELL-SIZE 30)
+(define ARROW-LENGTH 40)
+(define ARROW-SIZE 15)
+
+(define (square n)
+  (rectangle n n))
+
+(define (need-arrow? x)
+  (or (pair? x)
+      (< 2 (string-length (~a x)))))
+
+(define (pict-cell x)
+  (cond
+    [(need-arrow? x)
+     (cc-superimpose (square CELL-SIZE)
+                     (scale (filled-ellipse CELL-SIZE CELL-SIZE) 1/4))]
+    [else
+     (cc-superimpose (square CELL-SIZE)
+                     (text (~a x)))]))
+
+(define (pict-cons-cell pair)
+  (hc-append -1
+             (pict-cell (car pair))
+             (pict-cell (cdr pair))))
+
+(define (cdr-find _ p)
+  (values (- (pict-width p) (/ CELL-SIZE 2.0))
+          (/ CELL-SIZE 2.0)))
+
+(define (car-find p _)
+  (values (/ CELL-SIZE 2.0)
+          (/ CELL-SIZE 2.0)))
+
+(define (left-find p p1)
+  (values (- (pict-width p) (pict-width p1))
+          (/ CELL-SIZE 2.0)))
+
+(define (top-find p p1)
+  (values (/ CELL-SIZE 2.0)
+          (- (pict-height p) (pict-height p1))))
+
+(define (horizontal-combined p1 p2)
+  (ht-append ARROW-LENGTH p1 p2))
+
+(define (vertical-combined n p1 p2)
+  (vl-append (- (* (+ CELL-SIZE ARROW-LENGTH) n)
+                (pict-height p1))
+             p1 p2))
+
+(define (arrow-from-cdr p1 p2)
+  (pin-arrow-line ARROW-SIZE
+                  (horizontal-combined p1 p2)
+                  p1 cdr-find
+                  p2 left-find))
+
+(define (arrow-from-car n p1 p2)
+  (pin-arrow-line ARROW-SIZE
+                  (vertical-combined n p1 p2)
+                  p1 car-find
+                  p2 top-find))
+
+(define (pict-atom x)
+  (cc-superimpose (cellophane (filled-rectangle CELL-SIZE CELL-SIZE) 0)
+                  (text (~a x))))
+
+
+(define (cdr* lst)
+  (if (null? lst)
+      '()
+      (cdr lst)))
+
+(define (pict-sexp/helper sexp height-list fail)
+  (when (and (pair? height-list)
+             (<= 0 (car height-list)))
+    (fail))
+  (cond
+    [(pair? sexp)
+     (let*-values ([(cell) (pict-cons-cell sexp)]
+                   [(cell-1 height-list)
+                    (cond
+                      [(need-arrow? (cdr sexp))
+                       (let-values ([(pict-cdr cdr-height-list)
+                                     (pict-sexp/helper (cdr sexp)
+                                                       (cdr* height-list)
+                                                       fail)])
+                         (values (arrow-from-cdr cell pict-cdr)
+                                 (cons 0 cdr-height-list)))]
+                      [else (values cell (cons 0 (cdr* height-list)))])]
+                   [(cell-2 height-list)
+                    (cond
+                      [(need-arrow? (car sexp))
+                       (let retry ([len 1] [height-list (map sub1 height-list)])
+                         (let/cc escape
+                           (let/cc fail
+                             (let-values ([(pict-car height-list)
+                                           (pict-sexp/helper (car sexp)
+                                                             height-list
+                                                             fail)])
+                               (escape (arrow-from-car len cell pict-car)
+                                       (map (λ (x) (+ x len)) height-list))))
+                           (retry (add1 len) (map sub1 height-list))))]
+                      [else (values cell height-list)])])
+       (values (lt-superimpose cell-1 cell-2) height-list))]
+    [else
+     (values (pict-atom sexp) (cons 0 (cdr* height-list)))]))
+
+(define (pict-sexp sexp)
+  (define-values (result height-list)
+    (pict-sexp/helper sexp '() (λ () (error "pict-sexp: implementation error"))))
+  result)
+(provide pict-sexp)