019f8fd211
git-subtree-dir: users/wpcarro git-subtree-mainline:464bbcb15cgit-subtree-split:24f5a642afChange-Id: I6105b3762b79126b3488359c95978cadb3efa789
142 lines
4.1 KiB
EmacsLisp
142 lines
4.1 KiB
EmacsLisp
;;; number.el --- Functions for working with numbers -*- lexical-binding: t -*-
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;; Author: William Carroll <wpcarro@gmail.com>
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;; Version: 0.0.1
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;; Package-Requires: ((emacs "24"))
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;; Homepage: https://user.git.corp.google.com/wpcarro/briefcase
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;;; Commentary:
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;;
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;; Classifications of numbers:
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;; - Natural: (a.k.a positive integers, counting numbers); {1, 2, 3, ... }
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;;
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;; - Whole: Natural Numbers, plus zero; {0, 1, 2, 3, ...}
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;;
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;; - Integers: Whole numbers plus all the negatives of the natural numbers;
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;; {... , -2, -1, 0, 1, 2, ...}
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;;
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;; - Rational numbers: (a.k.a. fractions) where the top and bottom numbers are
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;; integers; e.g., 1/2, 3/4, 7/2, ⁻4/3, 4/1. Note: The denominator cannot be
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;; 0, but the numerator can be.
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;;
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;; - Real numbers: All numbers that can be written as a decimal. This includes
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;; fractions written in decimal form e.g., 0.5, 0.75 2.35, ⁻0.073, 0.3333, or
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;; 2.142857. It also includes all the irrational numbers such as π, √2 etc.
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;; Every real number corresponds to a point on the number line.
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;;
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;; The functions defined herein attempt to capture the mathematical definitions
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;; of numbers and their classifications as defined above.
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;;; Code:
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Dependencies
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(require 'prelude)
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(require 'dash)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Library
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(defconst number-test? t
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"When t, run the test suite defined herein.")
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;; TODO: What about int.el?
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;; TODO: How do we handle a number typeclass?
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(defun number-positive? (x)
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"Return t if `X' is a positive number."
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(> x 0))
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(defun number-negative? (x)
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"Return t if `X' is a positive number."
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(< x 0))
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;; TODO: Don't rely on this. Need to have 10.0 and 10 behave similarly.
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(defun number-float? (x)
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"Return t if `X' is a floating point number."
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(floatp x))
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(defun number-natural? (x)
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"Return t if `X' is a natural number."
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(and (number-positive? x)
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(not (number-float? x))))
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(defun number-whole? (x)
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"Return t if `X' is a whole number."
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(or (= 0 x)
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(number-natural? x)))
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(defun number-integer? (x)
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"Return t if `X' is an integer."
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(or (number-whole? x)
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(number-natural? (- x))))
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;; TODO: How defensive should these guards be? Should we assert that the inputs
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;; are integers before checking evenness or oddness?
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;; TODO: Look up Runar (from Unison) definition of handling zero as even or odd.
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;; TODO: How should rational numbers be handled? Lisp is supposedly famous for
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;; its handling of rational numbers.
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;; TODO: `calc-mode' supports rational numbers as "1:2" meaning "1/2"
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;; (defun number-rational? (x))
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;; TODO: Can or should I support real numbers?
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;; (defun number-real? (x))
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(defun number-even? (x)
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"Return t if `X' is an even number."
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(or (= 0 x)
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(= 0 (mod x 2))))
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(defun number-odd? (x)
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"Return t if `X' is an odd number."
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(not (number-even? x)))
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(defun number-dec (x)
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"Subtract one from `X'.
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While this function is undeniably trivial, I have unintentionally done (- 1 x)
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when in fact I meant to do (- x 1) that I figure it's better for this function
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to exist, and for me to train myself to reach for it and its inc counterpart."
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(- x 1))
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(defun number-inc (x)
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"Add one to `X'."
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(+ x 1))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Tests
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(when number-test?
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(prelude-assert
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(number-positive? 10))
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(prelude-assert
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(number-natural? 10))
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(prelude-assert
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(number-whole? 10))
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(prelude-assert
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(number-whole? 0))
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(prelude-assert
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(number-integer? 10))
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;; (prelude-assert
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;; (= 120 (number-factorial 5)))
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(prelude-assert
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(number-even? 6))
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(prelude-refute
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(number-odd? 6))
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(prelude-refute
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(number-positive? -10))
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(prelude-refute
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(number-natural? 10.0))
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(prelude-refute
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(number-natural? -10))
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(prelude-refute
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(number-natural? -10.0)))
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(provide 'number)
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;;; number.el ends here
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