citysworn/core.rkt

#lang racket

;; start with some basic utilities
(define (d n)
  (random 1 (+ n 1)))

;; the logic for judging the 'outcome' of an Ironsworn roll or progress track
(define (judge-outcome attempt challenge-1 challenge-2)
  (let [(outcome
         (cond [(and (> attempt challenge-1) (> attempt challenge-2))
                'success]
               [(or (> attempt challenge-1) (> attempt challenge-2))
                'partial]
               [else 'failure]))]
    `(,outcome ,attempt (,challenge-1 ,challenge-2))))
  

;; a typical Ironsworn roll:
(define (roll-plus-mod m)
  (let [
         ;; roll two challenge dice
         (challenge-1 (d 10))
         (challenge-2 (d 10))
         ;; roll an attempt die
         (attempt (+ (d 6) m))]
    ;; judge the outome
    (judge-outcome attempt challenge-1 challenge-2)))


;; this just keeps us honest that this is playable with dice
(define *allowed-table-sizes* '(2 4 6 8 10 12 20 36 50 100))

(define (oracle table)
  (cond [(andmap valid-oracle-result? table)
         (if (member (length table) *allowed-table-sizes*)
             (lambda () (car (shuffle table)))
             (error 'oracle "Length ~a is not a die-size-compatible length" (length table)))]
        [(andmap valid-table-member? table)
         (let [(max (max-table-size table))]
           (lambda () (table-index (d max) table)))]
        [else (error 'oracle "Unexpected argument: ~a" table)]))

(define (max-table-size table)
  (let [(final (last table))]
    (if (= (length final) 3) (cadr final) (car final))))

(define (valid-oracle-result? thing)
  (or (symbol? thing) (string? thing)))

(define (valid-table-member? member)
  (and (list? member)
       (or (and (= (length member) 3)
                (number? (car member))
                (number? (cadr member))
                (valid-oracle-result? (caddr member)))
           (and (= (length member) 2)
                (number? (car member))
                (valid-oracle-result? (cadr member))))))

(define (table-index idx table)
  (if (null? table)
      (error 'table-index "Unexpected empty table")
      (let [(head (car table))]
        (cond [(and (= (length head) 3)
                    (>= idx (car head))
                    (<= idx (cadr head)))
               (caddr head)]
              [(and (= (length head) 2)
                    (= idx (car head)))
               (cadr head)]
              [else (table-index idx (cdr table))]))))

(define-syntax-rule [define-oracle name . table]
  (define name (oracle (quote table))))

(provide judge-outcome roll-plus-mod oracle define-oracle)