janet/lib/pp.dst

# Implements a simple pretty printer. Offers similar functionality
# as the describe function.

(defn- pp-seq [pp seen buf a start end]
 (if (get seen a)
  (buffer-push-string buf "<cycle>")
  (do
   (put seen a true)
   (def len (length a))
   (buffer-push-string buf start)
   (for [i 0 len]
    (when (not= i 0) (buffer-push-string buf " "))
    (pp seen buf (get a i)))
   (buffer-push-string buf end)))
 buf)

(defn- pp-dict [pp seen buf a start end]
 (if (get seen a)
  (buffer-push-string buf "<cycle>")
  (do
   (put seen a true)
   (var k (next a nil))
   (buffer-push-string buf start)
   (while k
    (def v (get a k))
    (pp seen buf k)
    (buffer-push-string buf " ")
    (pp seen buf v)
    (varset! k (next a k))
    (when k (buffer-push-string buf " ")))
   (buffer-push-string buf end)))
 buf)

(def printers :private {
 :array  (fn [pp seen buf x] (pp-seq pp seen buf x "[" "]"))
 :tuple  (fn [pp seen buf x] (pp-seq pp seen buf x "(" ")"))
 :table  (fn [pp seen buf x] (pp-dict pp seen buf x "@{" "}"))
 :struct (fn [pp seen buf x] (pp-dict pp seen buf x "{" "}"))
})

(defn- default_printer [pp seen buf x] 
 (buffer-push-string buf (string x)) 
 buf)

(defn- pp1 [seen buf x]
  (def pmaybe (get printers (type x)))
  (def p (if pmaybe pmaybe default_printer))
  (p pp1 seen buf x))

(defn pp 
 "Pretty print a value x."
 [x] (print (pp1 @{} @"" x)))