1 files changed, 10 insertions, 16 deletions
diff --git a/AoC2023/day09/solver.lisp b/AoC2023/day09/solver.lisp
index 3df0cc3..647284f 100644
--- a/AoC2023/day09/solver.lisp
+++ b/AoC2023/day09/solver.lisp
@@ -13,32 +13,26 @@
 (defun terminal-p (row)
   (every #'= (cdr row) row))
 
-(defun get-coefs (row pick &optional acc)
+(defun get-coefs (row &optional (acc 0))
   (if (terminal-p row)
-      (nreverse (cons (funcall pick row) acc))
-      (get-coefs (row-reducer row) pick (cons (funcall pick row) acc))))
+      (+ (car (last row)) acc)
+      (get-coefs (row-reducer row) (+ (car (last row)) acc))))
 
 (defun parse-line (line)
   (mapcar #'parse-integer (uiop:split-string line)))
 
-(defun forward (line)
-  (reduce #'+ (get-coefs line (lambda (a) (car (last a))))))
-
-(defun backward (line)
-  (reduce #'- (get-coefs line #'car) :from-end t))
-
-(defun solver (lines key)
+(defun solver (lines order)
   (reduce #'+
-          (mapcar #'parse-line lines)
-          :key key))
+          lines
+          :key (alexandria:compose #'get-coefs order #'parse-line)))
 
 (fiveam:test solutions
   (fiveam:is (= 114 (solver (uiop:split-string eg-input :separator '(#\Newline))
-                            #'forward)))
+                            #'identity)))
   (fiveam:is (= 2105961943 (solver (uiop:read-file-lines "input")
-                                   #'forward)))
+                                   #'identity)))
 
   (fiveam:is (= 2 (solver (uiop:split-string eg-input :separator '(#\Newline))
-                          #'backward)))
+                          #'nreverse)))
   (fiveam:is (= 1019 (solver (uiop:read-file-lines "input")
-                             #'backward))))
+                             #'nreverse))))