lexer: Avoid 'fold-right'.

* gash/lexer.scm (join-contiguous-strings): Use 'fold' and 'reverse'
instead of 'fold-right'.

gash/lexer.scm

@@ -165,13 +165,16 @@
 
 (define (join-contiguous-strings lst)
   "Join all contiguous strings in @var{lst}."
-  (fold-right (lambda (x lst)
-                (let ((head (if (null? lst) #f (car lst))))
-                  (if (and (string? x) (string? head))
-                      (cons (string-append x head) (cdr lst))
-                      (cons x lst))))
-              '()
-              lst))
+  (match lst
+    (() lst)
+    ((head . rest)
+     (reverse
+      (fold (lambda (x acc)
+              (if (and (string? x) (string? (car acc)))
+                  (cons (string-append (car acc) x) (cdr acc))
+                  (cons x acc)))
+            (list head)
+            rest)))))
 
 (define-inlinable (next-char port)
   "Advance @var{port} by one character and return the lookahead