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;;; lib.functions.lisp - 2025-02-09
;; Copyright (C) 2025 Aryadev Chavali
;; This program is distributed in the hope that it will be useful, but WITHOUT
;; ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
;; FOR A PARTICULAR PURPOSE. See the GNU General Public License Version 2 for
;; details.
;; You may distribute and modify this code under the terms of the GNU General
;; Public License Version 2, which you should have received a copy of along with
;; this program. If not, please go to <https://www.gnu.org/licenses/>.
;;; Commentary:
;; Helpful functions for usage throughout the project.
;;; Code:
(in-package :lib.functions)
(fn range (start end &optional (step 1)) (-> (fixnum fixnum &optional fixnum) list)
"Make a list of numbers from START to END (exclusive). If STEP is given, then
each member is STEP distance apart."
(if (<= end start)
(error (format nil "~a < ~a" end start))
(loop :for i :from start :to (1- end) :by step
:collect i)))
(fn take (n lst) (-> (fixnum list) list)
"Return the first N elements of LST."
(subseq lst 0 n))
(fn split (n lst) (-> (fixnum list) list)
"Return CONS where CAR is the first N elements of LST and CDR is the rest."
(cons (take n lst)
(subseq lst n)))
(fn rev-map (indicator lst &key (key-eq #'eq))
(-> (function list &key (:key-eq function)) list)
"Given LST and INDICATOR: LST -> A, return an association list A -> 2^LST
where key x in A has associations {y in LST : INDICATOR(y) = x}."
(loop :with assoc-list := nil
:for element :in lst
:for key = (funcall indicator element)
:if (assoc key assoc-list :test key-eq)
:do (->> (alist-val key assoc-list)
(cons element)
(setf (alist-val key assoc-list)))
:else
:do (setq assoc-list (cons (list key element) assoc-list))
:finally (return assoc-list)))
(fn parse-integer* (inp) (-> (string) (or integer list))
"Given string INP, attempt to parse an integer. Return NIL otherwise."
(parse-integer inp :junk-allowed t))
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