From bb2466f19b17f59a6567bf827b5ecb6f4db7fc3d Mon Sep 17 00:00:00 2001
From: Colin Okay <cbeok@protonmail.com>
Date: Wed, 8 Jul 2020 11:00:51 -0500
Subject: added more constructors

---
 gtwiwtg.lisp | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

(limited to 'gtwiwtg.lisp')

diff --git a/gtwiwtg.lisp b/gtwiwtg.lisp
index 35b834c..535c175 100644
--- a/gtwiwtg.lisp
+++ b/gtwiwtg.lisp
@@ -93,6 +93,96 @@ the values passed as ARGS looped forever."
                             (declare (ignore state))
                             (values (random arg) nil))))
 
+
+(defun from-thunk (thunk &optional times)
+  "Creates a generator that produces an inifinte series of values that
+are the return value of (FUNCALL THUNK)
+
+If TIMES is supplied, THUNK will only be called TIMES times."
+  (let ((thunk-proxy (lambda (ignore) (declare (ignore ignore)) (funcall thunk))))
+    (map! thunk-proxy (range :to (when times (1- times))))))
+
+(defun from-recurrence (rec n-1 &rest n-m)
+  "Creates a generator from a recurrence relation. 
+
+REC is a function of K arguments.  
+
+The Nth value of the series generated by the new generator is the result of 
+calling REC on the previoius K results. 
+
+N-1 and N-M are used to initialize the recurrence. (1+ (LENGTH N-M))
+should be K, the number of arguments acepted by REC.
+
+Example
+
+> (let ((fibs (from-recurrence (lambda (n-1 n-2) (+ n-1 n-2)) 0 1)))
+     (take 10 fibs))
+
+(1 1 2 3 5 8 13 21 34 55)
+
+"
+  (let* ((history (cons n-1 n-m))
+         (thunk  (lambda ()
+                   (let ((nth (apply rec history)))
+                     (setf history (cons nth (butlast history)))
+                     nth))))
+    (from-thunk thunk)))
+
+(defun from-input-stream (stream stream-reader)
+  "Create a generator from a STREAM. 
+
+You must supply as STREAM-READER function that accepts the stream as
+its only argument and returns NIL if the stream has run out of input,
+Non-NIL otherwise.
+
+This function will close the stream when it reaches the end.
+
+A quirk is that the last value returned from this generator is NIL.
+
+Avoid using with TAKE or PICK-OUT as the file stream will not be closed."
+  (make-instance 'generator!
+                 :state stream
+                 :next-p-fn #'open-stream-p
+                 :next-fn (lambda (stream)
+                            (let ((val (funcall stream-reader stream)))
+                              (if val
+                                  (values val stream)
+                                  (progn
+                                    (close stream)
+                                    (values nil stream)))))))
+
+
+(defun file-lines (path)
+  "Creates a generator that produces the lines of a file.  The stream
+to the file is closed when the generator finishes.
+
+Returns NIL on the last iteration.  
+
+Avoid using with TAKE or PICK-OUT as the file stream will not be closed."
+  (from-input-stream (open path)
+                     (lambda (stream) (read-line stream nil nil))))
+
+(defun file-chars (path)
+  "Creates a generator that produces the characters of a file. The
+stream to the file is closed when the generator finishes.
+
+Returns NIL on the last iteration.
+
+Avoid using with TAKE or PICK-OUT as the file stream will not be closed.
+"
+  (from-input-stream (open path)
+                     (lambda (stream) (read-char stream nil nil))))
+
+(defun file-bytes (path)
+  "Creates a generator that produces the bytes of a file. The
+stream to the file is closed when the generator finishes.
+
+Returns NIL on the last iteration.
+
+Avoid using with TAKE or PICK-OUT as the file stream will not be closed."  
+  (from-input-stream (open path :element-type '(unsigned-byte 8))
+                     (lambda (stream) (read-byte stream nil nil))))
+
 ;;; Some utilities
 
 (defun all-different (things)
-- 
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