reimplemented map using reduce

day01-easy/main.scm

@@ -10,22 +10,22 @@
       '()
       (cons line (loop (read-line))))))
 
-(define (map list mapper)
+(define (reduce-right reducer initial list)
   (if
     (null? list)
-    '()
-    (cons (mapper (car list)) (map (cdr list) mapper))))
+    initial
+    (reducer (car list) (reduce-right reducer initial (cdr list)))))
 
-(define (reduce list reducer current)
-  (if
-    (null? list)
-    current
-    (reduce (cdr list) reducer (reducer current (car list)))))
+(define (map mapper list)
+  (reduce-right
+    (lambda (current accumulator) (cons (mapper current) accumulator))
+    '()
+    list))
 
-(define (combine a b combiner)
+(define (combine combiner a b)
   (if (null? a) b (if (null? b) a (combiner a b))))
 
-(define (sum numbers) (reduce numbers + 0))
+(define (sum numbers) (reduce-right + 0 numbers))
 
 (define
   (repeat value number)
@@ -36,23 +36,25 @@
 
 (define (is-numeric-char char) (if (char-numeric? char) #t #f))
 
-(define (first-last list predicate)
-  (reduce
-    (map list (lambda (entry)
-      (if (predicate entry) (repeat entry 2) '())))
+(define (first-last predicate list)
+  (reduce-right
     (lambda (current accumulator)
       (combine
+        (lambda (left right) (cons (car left) (cdr right)))
         current
-        accumulator
-        (lambda (current rest) (cons (car current) (cdr rest)))))
-    '()))
+        accumulator))
+    '()
+    (map
+      (lambda (entry)
+        (if (predicate entry) (repeat entry 2) '()))
+      list)))
 
 (define (solve-line line)
   ((lambda (first-last-result)
     (string->number (list->string first-last-result)))
-    (first-last (string->list line) is-numeric-char)))
+    (first-last is-numeric-char (string->list line))))
 
 (define (solve-all lines)
-  (sum (map lines solve-line)))
+  (sum (map solve-line lines)))
 
 (display (solve-all (read-lines)))