[elpa] externals/stream daa19594e7 3/7: Add generalized variables for streams that error when used.

[Stefan Monnier]

branch: externals/stream
commit daa19594e7058ae531ec611b067fb970353b0e7c
Author: Earl Hyatt <okamsn@protonmail.com>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    Add generalized variables for streams that error when used.
    
    * stream.el (seq-elt, stream-first, stream-rest): Signal an error when 
trying to
    use this function as a place for 'setf'.
---
 stream.el | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/stream.el b/stream.el
index 300f3b8ae2..dea42b4962 100644
--- a/stream.el
+++ b/stream.el
@@ -290,6 +290,10 @@ range is infinite."
 Return nil if STREAM is empty."
   (stream--first (stream--force stream)))
 
+(defun \(setf\ stream-first\) (_store _stream)
+  "Signal an error when trying to use `setf' on the head of a stream."
+  (error "Streams are not mutable"))
+
 (defun stream-rest (stream)
   "Return a stream of all but the first element of STREAM."
   (setq stream (stream--force stream))
@@ -297,6 +301,10 @@ Return nil if STREAM is empty."
       (stream-empty)
     (stream--rest stream)))
 
+(defun \(setf\ stream-rest\) (_store _stream)
+  "Signal an error when trying to use `setf' on the tail of a stream."
+  (error "Streams are not mutable"))
+
 (defun stream-append (&rest streams)
   "Concatenate the STREAMS.
 Requesting elements from the resulting stream will request the
@@ -337,6 +345,9 @@ elements in the STREAMS in order."
     (setq n (1- n)))
   (stream-first stream))
 
+(cl-defmethod (setf seq-elt) (_store (_sequence stream) _n)
+  (error "Streams are not mutable"))
+
 (cl-defmethod seq-length ((stream stream))
   "Return the length of STREAM.
 This function will eagerly consume the entire stream."