AdventOfCode-2023-functional/day05-easy/main.scm

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

;=============== functions with side effects (I/O) ======================
(use-modules (ice-9 rdelim))

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

(define (display-ln value) (list (display value) (display "\n")))

(define (assert-eq error-message expected actual)
  (if (not (equal? expected actual))
    (display-ln (list error-message (list "expected" expected) (list "actual" actual)))
    '()))

(define (tee value) (car (list value (display-ln value))))
(define (tee-with-comment comment) (lambda (value) (car (list value (display comment) (display " ") (display-ln value)))))
;=============== end of functions with side effects ======================

(define (id value) value)
(define (is value) (lambda (x) (equal? x value)))
(define (is-not value) (lambda (x) (not (equal? x value))))
(define (is-not-empty value) (not (null? value)))

;=============== prepend ======================
(define (prepend first-value) (lambda (rest) (cons first-value rest)))

(assert-eq "prepend test failed"
  '(1 2 3 4)
  ((prepend 1) '(2 3 4)))

;=============== combinators ======================
(define (Y f) (f (lambda (x) ((Y f) x))))
(define (Y2 f) (f (lambda (x y) ((Y2 f) x y))))

(assert-eq "Y test 1 (factorial) failed"
  120
  ((Y (lambda (f) (lambda (n) (if (= n 0) 1 (* n (f (- n 1))))))) 5))

(assert-eq "Y2 test 1 (pascal triangle) failed"
  35
  ((Y2 (lambda (f) (lambda (a b)
    (if (= a 0) 1 (if (= b 0) 1 (+ (f (- a 1) b) (f a (- b 1))))))))
    3 4))

;=============== reduce-right ======================
(define (reduce-right initial reducer) (Y
  (lambda (f) (lambda (values)
    (if (null? values) initial (reducer (car values) (f (cdr values))))))))

(assert-eq "reduce-right test 1 failed"
  '(4 101 3 102 2 103 1 104 0)
  ((reduce-right '(0)
    (lambda (current accumulator) (cons (+ 1 (car accumulator)) (cons current accumulator))))
    '(101 102 103 104)))

;=============== reduce-left ======================
(define (reduce-left initial reducer)
  (lambda (values)
    ((Y2
      (lambda (f) (lambda (rest accumulator)
        (if (null? rest) accumulator (f (cdr rest) (reducer (car rest) accumulator))))))
      values
      initial)))

(assert-eq "reduce-left test 1 failed"
  '(4 104 3 103 2 102 1 101 0)
  ((reduce-left '(0)
    (lambda (current accumulator) (cons (+ 1 (car accumulator)) (cons current accumulator))))
    '(101 102 103 104)))

;=============== reverse ======================
(define reverse (reduce-left '() cons))

(assert-eq "reverse test 1 failed"
  '(4 3 2 1)
  (reverse '(1 2 3 4)))

;=============== map ======================
(define (map mapper) (reduce-right '()
  (lambda (current accumulator) (cons (mapper current) accumulator))))

(assert-eq "map test 1 failed"
  '(1 4 9 16)
  ((map (lambda (x) (* x x)))
    '(1 2 3 4)))

(assert-eq "map test 2 failed"
  '(1 2 (3 4) 5)
  ((map id) '(1 2 (3 4) 5)))

;=============== concat ======================
(define (concat left right)
  ((reduce-right right (lambda (current accumulator) (cons current accumulator)))
    left))

(assert-eq "concat test 1 failed"
  '(1 2 3 4 5)
  (concat '(1 2) '(3 4 5)))

;=============== flat ======================
(define flat (reduce-right '() concat))

(assert-eq "flat test 1 failed"
  '(1 2 3 4 5 (6 7) 8)
  (flat '((1 2) () (3 4) (5 (6 7) 8))))

;=============== filter ======================
(define (filter predicate) (reduce-right '()
  (lambda (current accumulator)
    (if (predicate current) (cons current accumulator) accumulator))))

(assert-eq "filter test 1 failed"
  '(2 4 4 2)
  ((filter (lambda (x) (= (modulo x 2) 0)))
    '(1 2 3 4 4 3 2 1)))

;=============== first ======================
(define (first predicate) (reduce-right '()
  (lambda (current accumulator)
    (if (predicate current) current accumulator))))

(assert-eq "first with is-not-empty test 1 failed"
  '(1 2 3)
  ((first is-not-empty) '(() (1 2 3))))

;=============== coalesce ======================
(define (coalesce-not-empty default-lazy) (lambda (value) (if (null? value) (default-lazy) value)))

(assert-eq "coalesce-not-empty test 1 failed"
  '(1)
  ((coalesce-not-empty (lambda () '(1))) '()))

(assert-eq "coalesce-not-empty test 2 failed"
  '(2)
  ((coalesce-not-empty (lambda () '(1))) '(2)))

(assert-eq "coalesce-not-empty test 3 failed (wrong result)"
  '(2)
  ((coalesce-not-empty (lambda () (display-ln "coalesce-not-empty test 3 failed (called default-lazy)")))
    '(2)))

;=============== truthy-chaining ======================
(define (truthy-chaining f) (lambda (value) (if value (f value) #f)))

(assert-eq "coalesce-not-empty test 1 failed"
  2
  ((truthy-chaining (lambda (x) (+ x 1))) 1))

(assert-eq "coalesce-not-empty test 2 failed"
  #f
  ((truthy-chaining (lambda (x) (+ x 1))) #f))

;=============== compose-two ======================
(define (compose-two f g) (lambda (x) (f (g x))))

(assert-eq "compose-two test 1 failed"
  6
  ((compose-two
    (lambda (x) (* x 2))
    (lambda (x) (+ x 2)))
    1))

;=============== compose ======================
(define compose (reduce-right id compose-two))

(assert-eq "compose test 1 failed"
  '(1 2 3 4)
  ((compose (list
    (prepend 1)
    (prepend 2)
    (prepend 3)))
    '(4)))

;=============== compose ======================
(define (combine combiner)
  (lambda (a b) (if (null? a) b (if (null? b) a (combiner a b)))))

(assert-eq "combine test 1 failed"
  '(1 3)
  ((combine (lambda (a b) (list (car a) (car b))))
    '(1 2)
    '(3 4)))

(assert-eq "combine test 1 failed"
  '(1 2)
  ((combine (lambda (a b) (list (car a) (car b))))
    '(1 2)
    '()))

(assert-eq "combine test 1 failed"
  '(3 4)
  ((combine (lambda (a b) (list (car a) (car b))))
    '()
    '(3 4)))

(assert-eq "combine test 1 failed"
  '()
  ((combine (lambda (a b) (list (car a) (car b))))
    '()
    '()))

;=============== sum ======================
(define sum (reduce-right 0 +))

(assert-eq "sum test 1 failed"
  6
  (sum '(1 2 3)))

;=============== min-list ======================
(define min-list
  (reduce-right #f
    (lambda (current accumulator)
      (if accumulator (min current accumulator) current))))

(assert-eq "min-list test 1 failed"
  2
  (min-list '(7 3 8 5 2 6 9)))

(assert-eq "min-list test 2 failed"
  #f
  (min-list '()))

;=============== repeat ======================
(define (repeat value) (Y
  (lambda (f) (lambda (n)
    (if (= n 0) '() (cons value (f (- n 1))))))))

(assert-eq "repeat test 1 failed"
  '(1 1 1)
  ((repeat 1) 3))

;=============== value-by-index ======================
(define value-by-index (Y2
  (lambda (f) (lambda (values index)
    (if (= index 0) (car values) (f (cdr values) (- index 1)))))))

(assert-eq "value-by-index test 1 failed"
  12
  (value-by-index '(10 11 12 13 14) 2))

;=============== split ======================
(define (split predicate)
  (reduce-right '(())
    (lambda (current accumulator)
      (if
        (predicate current)
        (cons '() accumulator)
        (cons (cons current (car accumulator)) (cdr accumulator))))))

(assert-eq "split test 1 failed"
  '((1 2) (3 4 5) (6 7))
  ((split (is 0))
    '(1 2 0 3 4 5 0 6 7)))

(assert-eq "split test 2 failed"
  '(() (1 2) () (3 4 5) (6 7) ())
  ((split (is 0))
    '(0 1 2 0 0 3 4 5 0 6 7 0)))

;=============== solution ======================
(define symbol-current (quote current))
(define symbol-previous (quote previous))

(define parse-initial
  (compose (list
    (map (compose (list
      (lambda (number) (list symbol-current number))
      string->number
      list->string)))
    cdr
    (split (is #\space))
    string->list)))

(define (mark-state-value-previous state-entry) (cons symbol-previous (cdr state-entry)))
(define (is-state-value-current state-entry) (equal? symbol-current (car state-entry)))
(define (get-state-value state-entry) (car (cdr state-entry)))
(define swap-state (compose (list
  #!(tee-with-comment "state after swap")!#
  (map mark-state-value-previous)
  (filter is-state-value-current)
  #!(tee-with-comment "state before swap")!#)))

(define (create-map numbers) (list
  ;; convert it from destination_start, source_start, length
  ;; to source_start, source_end, destination_start
  (value-by-index numbers 1)
  (+ (value-by-index numbers 1) (value-by-index numbers 2))
  (value-by-index numbers 0)))

(define (map-source-start seed-map) (value-by-index seed-map 0))
(define (map-source-end seed-map) (value-by-index seed-map 1))
(define (map-destination-start seed-map) (value-by-index seed-map 2))

(define (apply-map-to-previous-state-value seed-map state-value)
  (if
    (and
      (<= (map-source-start seed-map) state-value)
      (< state-value (map-source-end seed-map)))
    (list symbol-current (+ (- state-value (map-source-start seed-map)) (map-destination-start seed-map)))
    (list symbol-previous state-value)))

(define (apply-map-to-state-entry seed-map)
  (lambda (state-entry)
    (if
      (is-state-value-current state-entry)
      state-entry
      (apply-map-to-previous-state-value seed-map (get-state-value state-entry)))))

(define (apply-map-to-state seed-map)
  (map (apply-map-to-state-entry seed-map)))

(define (seed-maps-processor raw-seed-maps)
  (compose (list
    ;; for state
    #!(tee-with-comment "state after applying mapset")!#
    ((compose (list
      ;; for list of map lines (within a single map set); should return state-transforming lambda
      compose
      (map apply-map-to-state)
      #!(tee-with-comment "current mapset")!#
      (prepend '(0 4294967295 0))
      (map (compose (list
        ;; for map line
        create-map
        (map (compose (list
          ;; for number in map line
          string->number
          list->string)))
        (split (is #\space))
        string->list
      )))
      #!(tee-with-comment "raw seed maps without prefix")!#
      cdr))
      raw-seed-maps)
    swap-state)))

(define (final-state lines)
  (((compose (list
    compose
    (map seed-maps-processor)
    reverse
    (filter is-not-empty)
    (split (is ""))))
    (cdr lines))
    (parse-initial (car lines))))

(define solve-all
  (compose (list
    min-list
    (map get-state-value)
    (filter is-state-value-current)
    final-state)))

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