109 lines
2.4 KiB
Markdown
109 lines
2.4 KiB
Markdown
# Data Structures
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These functions operate on various data structures in Keithlisp.
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## `cons`
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```
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(cons car cdr)
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```
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`cons` allocates and returns a new cons with the given `car` and `cdr`.
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## `car`
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```
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(car cons)
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```
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`car` returns the car portion of `cons`, or nil if the argument is not a
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cons.
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## `cdr`
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```
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(cdr cons)
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```
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`cdr` returns the cdr portion of `cons`, or nil if the argument is not a
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cons.
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## `rplaca`
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```
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(rplaca cons value)
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```
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`rplaca` changes the car portion of `cons` to `value`. It returns the
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same `cons` it was given.
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## `rplacd`
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```
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(rplacd cons value)
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```
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`rplacd` changes the cdr portion of `cons` to `value`. It returns the
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same `cons` it was given.
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## `list`
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```
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(list &rest elements)
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```
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`list` allocates and returns a new list containing `elements`.
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## `length`
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```
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(length list)
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```
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`length` returns the length of `list`, or nil if it is not a valid list.
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**If `list` is circular, `length` will go into an infinite loop.**
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## `nth`
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```
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(nth index list)
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```
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`nth` returns the `index`th element in `list`. `index` must be an int.
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If `index` is negative, `nth` will add `(length list)` to it. **This
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will fail if `list` is circular.**
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## `nthcdr`
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```
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(nthcdr index list)
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```
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`nthcdr` returns the cdr of the `index`th cons in `list`. `index` must
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be an int.
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If `index` is negative, `nthcdr` will add `(length list)` to it. **This
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will fail if `list` is circular.**
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## `append`
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```
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(append &rest lists)
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```
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`append` constructs a new list containing all the elements of `lists`
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appended together. It makes a shallow copy of each of its arguments.
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## `push`
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```
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(push list item)
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```
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`push` pushes `item` onto `list` and returns the new head of `list`.
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## `assoc`
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```
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(assoc alist key)
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```
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`assoc` returns the first cons in `alist` whose car is
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[`eq`](stdlib_comparison.md#eq) to `key`, or nil if no matching cons
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was found.
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## `rassoc`
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```
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(rassoc alist value)
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```
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`rassoc` returns the first cons in `alist` whose cdr is
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[`eq`](stdlib_comparison.md#eq) to `value`, or nil if no matching cons
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was found.
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## `alist-put`
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```
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(alist-put alist key value)
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```
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`alist-put` creates a new cons mapping `key` to `value`, and attempts to
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update `alist` with it in-place. If `alist` already contains a cons
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whose car is [`eq`](stdlib_comparison.md#eq) to `key`, the cons is
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replaced in-place with the new one. Otherwise, `alist-put` pushes the
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new cons onto `alist` and returns the new head of `alist`, in the same
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manner as [`push`](stdlib_data.md#push).
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