srfi-1: Rewrite 'find' in Scheme.

This halves the wall-clock time of:

  guile -c '(use-modules (srfi srfi-1)) (define lst (make-list 100000000 1)) (find zero? lst)'

and yields an 18% speedup on:

  guile -c '(use-modules (srfi srfi-1)) (define lst (make-list 100000000 1)) (find (lambda (x) (= 2 x)) lst)'

* libguile/srfi-1.c (scm_srfi1_find): Remove.
* libguile/srfi-1.h (scm_srfi1_find): Likewise.
* module/srfi/srfi-1.scm (find): New procedure.
* doc/ref/srfi-modules.texi (SRFI-1 Searching): Adjust docstring.

1 files changed, 12 insertions, 1 deletions

diff --git a/module/srfi/srfi-1.scm b/module/srfi/srfi-1.scm
index c0ee53548..e5b28e777 100644
--- a/module/srfi/srfi-1.scm
+++ b/module/srfi/srfi-1.scm
@@ -1,6 +1,6 @@
 ;;; srfi-1.scm --- List Library
 
-;; 	Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2009, 2010, 2011, 2014 Free Software Foundation, Inc.
+;; 	Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2009, 2010, 2011, 2014, 2020 Free Software Foundation, Inc.
 ;;
 ;; This library is free software; you can redistribute it and/or
 ;; modify it under the terms of the GNU Lesser General Public
@@ -720,6 +720,17 @@ the list returned."
 
 ;;; Searching
 
+(define (find pred lst)
+  "Return the first element of @var{lst} that satisfies the predicate
+@var{pred}, or return @code{#f} if no such element is found."
+  (check-arg procedure? pred find)
+  (let loop ((lst lst))
+    (and (not (null? lst))
+         (let ((head (car lst)))
+           (if (pred head)
+               head
+               (loop (cdr lst)))))))
+
 (define (take-while pred ls)
   "Return a new list which is the longest initial prefix of LS whose
 elements all satisfy the predicate PRED."