From 95b46cfc463be0371f62400912656106f8e3d0cb Mon Sep 17 00:00:00 2001
From: Calvin Rose <calsrose@gmail.com>
Date: Sat, 22 Sep 2018 14:17:47 -0400
Subject: [PATCH] Add lazyseqs code back.

---
 lib/lazyseqs.janet | 142 +++++++++++++++++++++++++++++++++------------
 1 file changed, 104 insertions(+), 38 deletions(-)

diff --git a/lib/lazyseqs.janet b/lib/lazyseqs.janet
index 23bf9c2d..7de444bd 100644
--- a/lib/lazyseqs.janet
+++ b/lib/lazyseqs.janet
@@ -1,41 +1,107 @@
-# Ansi terminal colors
+# An example implementation of functional, lazy
+# sequences, as in clojure. The lazy seq is essentially
+# A lazy linked list, where the next value is a function
+# that must be called (realizing it), and the memoized.
+# Use with (import "./path/to/this/file" :prefix "seq.")
 
-(def- colormap
-  {:black 30
-   :bg-black 40
-   :red 31
-   :bg-red 41
-   :green 32
-   :bg-green 42
-   :yellow 33
-   :bg-yellow 43
-   :blue 34
-   :bg-blue 44
-   :magenta 35
-   :bg-magenta 45
-   :cyan 36
-   :bg-cyan 46
-   :white 37
-   :bg-white 47
+(defmacro delay [& forms]
+  "Lazily evaluate a series of expressions. Returns a function that
+  returns the result of the last expression. Will only evaluate the
+  body once, and then memoizes the result."
+  (def $state (gensym))
+  (def $loaded (gensym))
+  (tuple 'do
+         (tuple 'var $state nil)
+         (tuple 'var $loaded nil)
+         (tuple 'fn (array)
+                (tuple 'if $loaded
+                       $state
+                       (tuple 'do
+                              (tuple ':= $loaded true)
+                              (tuple ':= $state (tuple.prepend forms 'do)))))))
 
-   :bright-black 90
-   :bg-bright-black 100
-   :bright-red 91
-   :bg-bright-red 101
-   :bright-green 92
-   :bg-bright-green 102
-   :bright-yellow 93
-   :bg-bright-yellow 103
-   :bright-blue 94
-   :bg-bright-blue 104
-   :bright-magenta 95
-   :bg-bright-magenta 105
-   :bright-cyan 96
-   :bg-bright-cyan 106
-   :bright-white 97
-   :bg-bright-white 107})
+# Use tuples instead of structs to save memory
+(def HEAD :private 0)
+(def TAIL :private 1)
 
-(loop [[name color] :in (pairs colormap)]
-  (defglobal (string.slice name 1)
-    (fn color-wrapper [& pieces]
-      (string "\e[" color "m" (apply1 string pieces) "\e[0m"))))
+(defn empty-seq
+  "The empty sequence."
+  [] nil)
+
+(defmacro cons
+  "Create a new sequence by prepending a value to the original sequence."
+  [h t]
+  (def x (tuple h t))
+  (fn [] x))
+
+(defn empty?
+  "Check if a sequence is empty."
+  [s]
+  (not (s)))
+
+(defn head
+  "Get the next value of the sequence."
+  [s]
+  (get (s) HEAD))
+
+(defn tail
+  "Get the rest of a sequence"
+  [s]
+  (get (s) TAIL))
+
+(defn range2
+  "Return a sequence of integers [start, end)."
+  [start end]
+  (if (< start end)
+    (delay (tuple start (range2 (+ 1 start) end)))
+    empty-seq))
+
+(defn range
+  "Return a sequence of integers [0, end)."
+  [end]
+  (range2 0 end))
+
+(defn map
+  "Return a sequence that is the result of applying f to each value in s."
+  [f s]
+  (delay
+    (def x (s))
+    (if x (tuple (f (get x HEAD)) (map f (get x TAIL))))))
+
+(defn realize
+  "Force evaluation of a lazy sequence."
+  [s]
+  (when (s) (realize (tail s))))
+
+(defn realize-map [f s]
+  "Evaluate f on each member of the sequence. Forces evaluation."
+  (when (s) (f (head s)) (realize-map f (tail s))))
+
+(defn drop
+  "Ignores the first n values of the sequence and returns the rest."
+  [n s]
+  (delay
+    (def x (s))
+    (if (and x (pos? n)) ((drop (- n 1) (get x TAIL))))))
+
+(defn take
+  "Returns at most the first n values of s."
+  [n s]
+  (delay
+    (def x (s))
+    (if (and x (pos? n))
+      (tuple (get x HEAD) (take (- n 1) (get x TAIL))))))
+
+(defn randseq
+  "Return a sequence of random numbers."
+  []
+  (delay (tuple (random) (randseq))))
+
+(defn take-while
+  "Returns a sequence of values until the predicate is false."
+  [pred s]
+  (delay
+    (def x (s))
+    (when x
+      (def thehead (get HEAD x))
+      (if thehead (tuple thehead (take-while pred (get TAIL x)))))))