81 lines
2.4 KiB
EmacsLisp
81 lines
2.4 KiB
EmacsLisp
;;; vector.el --- Working with Elisp's Vector data type -*- lexical-binding: t -*-
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;; Author: William Carroll <wpcarro@gmail.com>
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;;; Commentary:
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;; It might be best to think of Elisp vectors as tuples in languages like
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;; Haskell or Erlang.
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;;
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;; Not surprisingly, this API is modelled after Elixir's Tuple API.
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;;
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;; Some Elisp trivia:
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;; - "Array": Usually means vector or string.
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;; - "Sequence": Usually means list or "array" (see above).
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;;
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;; It might be a good idea to think of Array and Sequence as typeclasses in
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;; Elisp. This is perhaps more similar to Elixir's notion of the Enum protocol.
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;;
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;; Intentionally not supporting a to-list function, because tuples can contain
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;; heterogenous types whereas lists should contain homogenous types.
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;;; Code:
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;; TODO: Consider supporting an alias named tuple for vector.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Library
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(defconst vector/enable-tests? t
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"When t, run the tests defined herein.")
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;; TODO: Consider labelling variadic functions like `vector/concat*'
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;; vs. `vector/concat'.
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(defun vector/concat (&rest args)
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"Return a new vector composed of all vectors in `ARGS'."
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(apply #'vconcat args))
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;; TODO: Here's a sketch of a protocol macro being consumed.
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;; (definstance monoid vector
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;; :empty (lambda () []))
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(defun vector/prepend (x xs)
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"Add `X' to the beginning of `XS'."
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(vector/concat `[,x] xs))
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(defun vector/append (x xs)
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"Add `X' to the end of `XS'."
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(vector/concat xs `[,x]))
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(defun vector/get (i xs)
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"Return the value in `XS' at index, `I'."
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(aref xs i))
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(defun vector/set (i v xs)
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"Set index `I' to value `V' in `XS'.
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Returns a copy of `XS' with the updates."
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(let ((copy (vconcat [] xs)))
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(aset copy i v)
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copy))
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(defun vector/set! (i v xs)
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"Set index `I' to value `V' in `XS'.
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This function mutates XS."
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(aset xs i v))
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(when vector/enable-tests?
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(let ((xs [1 2 3])
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(ys [1 2 3]))
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(prelude/assert (= 1 (vector/get 0 ys)))
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(vector/set 0 4 ys)
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(prelude/assert (= 1 (vector/get 0 ys)))
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(prelude/assert (= 1 (vector/get 0 xs)))
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(vector/set! 0 4 xs)
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(prelude/assert (= 4 (vector/get 0 xs)))))
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;; TODO: Decide between "remove" and "delete" as the appropriate verbs.
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;; TODO: Implement this.
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;; (defun vector/delete (i xs)
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;; "Remove the element at `I' in `XS'.")
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(provide 'vector)
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;;; vector.el ends here
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