[PATCH] Add peek-error, pke.

[Janneke Nieuwenhuizen <janneke@gnu.org>]

Debuging using `pk' is popular in Guile, but not really usable if your
program is as (pseudo-)filter, i.e., writing its output to stdout.

* module/ice-9/boot-9.scm (peek-error, pke): New procedures.
---
 module/ice-9/boot-9.scm | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/module/ice-9/boot-9.scm b/module/ice-9/boot-9.scm
index 378ae2457..c4ee2b383 100644
--- a/module/ice-9/boot-9.scm
+++ b/module/ice-9/boot-9.scm
@@ -183,6 +183,16 @@ This is handy for tracing function calls, e.g.:
 
 (define pk peek)
 
+(define (peek-error . stuff)
+  "Like PEEK (PK), writing to (CURRENT-ERROR-PORT)."
+  (newline (current-error-port))
+  (display ";;; " (current-error-port))
+  (write stuff (current-error-port))
+  (newline (current-error-port))
+  (car (last-pair stuff)))
+
+(define pke peek-error)
+
 (define (warn . stuff)
   (newline (current-warning-port))
   (display ";;; WARNING " (current-warning-port))
-- 
2.45.1