AdventOfCode-2023-functional/day01-easy/main.scm

#!/usr/bin/guile -s
!#

(use-modules (ice-9 rdelim))

(define (read-lines)
  (let loop ((line (read-line)))
    (if
      (eof-object? line)
      '()
      (cons line (loop (read-line))))))

(define (map list mapper)
  (if
    (null? list)
    '()
    (cons (mapper (car list)) (map (cdr list) mapper))))

(define (reduce list reducer current)
  (if
    (null? list)
    current
    (reduce (cdr list) reducer (reducer current (car list)))))

(define (combine list combiner)
  (if
    (null? (car list))
    (cdr list)
    (if
      (null? (cdr list))
      (car list)
      (combiner (car list) (cdr list)))))

(define (sum numbers) (reduce numbers + 0))

(define
  (repeat value number)
  (if
    (= number 0)
    '()
    (cons value (repeat value (- number 1)))))

(define (is-numeric-char char) (if (char-numeric? char) #t #f))

(define (first-last list predicate)
  (if
    (null? list)
    '()
    (combine
      (cons
        (if
          (predicate (car list))
          (repeat (car list) 2)
          '())
        (first-last (cdr list) predicate))
      (lambda (current rest)
        (cons (car current) (cdr rest))))))

(define (solve-line line)
  (
    (lambda (first-last-result) (string->number (list->string first-last-result)))
    (first-last (string->list line) is-numeric-char)))

(define (solve-all lines)
  (sum (map lines solve-line)))

(display (solve-all (read-lines)))