| author |
Steve Losh <steve@stevelosh.com> |
| date |
Mon, 21 Dec 2020 20:51:12 -0500 |
| parents |
6f43a660d22a |
| children |
(none) |
(in-package :temperance.utils)
(defmacro push-if-new (thing place
&environment env
&key key (test '#'eql))
"Push `thing` into the list at `place` if it's not already there.
Returns whether `thing` was actually pushed. This function is basically
`pushnew` except for the return value.
"
(multiple-value-bind (temps exprs stores store-expr access-expr)
(get-setf-expansion place env)
(declare (ignore stores store-expr))
(with-gensyms (current result)
`(let* (,@(zip temps exprs)
(,current ,access-expr)
(,result (pushnew ,thing ,place :key ,key :test ,test)))
(not (eql ,current ,result))))))
(defun invert-hash-table (hash-table)
"Jesus christ don't actually use this for anything but debugging.
Inverts the keys/values of a `hash-table`.
"
(alist-to-hash-table
(loop :for k :being :the :hash-keys :of hash-table
:using (hash-value v)
:collect (list v k))))
(defmacro recursively (bindings &body body)
"Execute body recursively, like Clojure's `loop`/`recur`.
`bindings` should contain a list of symbols and (optional) default values.
In `body`, `recur` will be bound to the function for recurring.
Example:
(defun length (some-list)
(recursively ((list some-list) (n 0))
(if (null list)
n
(recur (cdr list) (1+ n)))))
"
(flet ((extract-var (binding)
(if (atom binding) binding (first binding)))
(extract-val (binding)
(if (atom binding) nil (second binding))))
`(labels ((recur ,(mapcar #'extract-var bindings)
,@body))
(recur ,@(mapcar #'extract-val bindings)))))
(defmacro ensure-aref (array index default-form)
"Get `index` in `array`, initializing if necessary.
If `index` is non-nil in `array`: return its value without evaluating
`default-form` at all.
If `index` is nil in `array`: evaluate `default-form` and set it before
returning it.
"
(once-only (index array)
`(or (aref ,array ,index)
(setf (aref ,array ,index) ,default-form))))
(defun megabytes (n)
"Return the number of 64-bit words in `n` megabytes."
(* 1024 1024 1/8 n))
;;;; Queues
;;; Based on the PAIP queues (thanks, Norvig), but beefed up a little bit to add
;;; tracking of the queue size.
(declaim (inline make-queue enqueue dequeue queue-empty-p))
(defstruct (queue (:constructor make-queue%))
(contents nil :type list)
(last nil :type list)
(size 0 :type fixnum))
(defun make-queue ()
(make-queue%))
(defun queue-empty-p (q)
(zerop (queue-size q)))
(defun enqueue (item q)
(let ((cell (cons item nil)))
(setf (queue-last q)
(if (queue-empty-p q)
(setf (queue-contents q) cell)
(setf (cdr (queue-last q)) cell))))
(incf (queue-size q)))
(defun dequeue (q)
(when (zerop (decf (queue-size q)))
(setf (queue-last q) nil))
(pop (queue-contents q)))
(defun queue-append (q l)
(loop :for item :in l
:for size = (enqueue item q)
:finally (return size)))
;;;; Lookup Tables
(defmacro define-lookup
(name (key value-type default) documentation &rest entries)
"Define a lookup function.
This macro defines a function that looks up a result in a constant array.
It's useful for things where you're looking up keys that are small integers,
like opcodes.
The function should be compiled to a few ASM instructions to read from a bit
of memory in O(1) time, instead of a huge list of CMP instructions that's
O(n) on the number of possibilities.
`name` should be a symbol that will become the name of the function. It will
be munged to make a name for the constant table too, but you shouldn't mess
with that.
`key` should be a symbol that will be used as the argument for the lookup
function.
`value-type` should be the type of your results.
`default` should be a value that will be returned from your function if a key
that does not exist is requested. Note that this same `eq` value will always
be returned.
`entries` should be the list of `(key value)` entries for the table.
Note that `key`, `default`, and all the keys of `entries` must be
macroexpansion-time constants!
"
(let ((max (reduce #'max entries :key #'car))
(entries (apply #'append entries)))
(let ((table (intern (format nil "+~A-TABLE+" name))))
`(progn
(define-constant ,table
(make-array (1+ ,max)
:element-type ',value-type
:initial-contents
(list ,@(loop :for i :from 0 :to max
:collect (getf entries i default))))
:test (lambda (x y) (declare (ignore x y)) t)) ; what could go wrong
(declaim (inline ,name))
(defun ,name (,key)
,documentation
(the ,value-type (aref ,table ,key)))))))
;;;; ecase/tree
;;; See http://www.foldr.org/~michaelw/log/programming/lisp/icfp-contest-2006-vm
(defmacro ecase/tree (keyform &body cases)
(labels ((%case/tree (keyform cases)
(if (<= (length cases) 4)
`(ecase ,keyform ,@cases)
(loop for rest-cases on cases
repeat (truncate (length cases) 2)
collect (first rest-cases) into first-half
finally (return `(if (< ,keyform ,(caar rest-cases))
,(%case/tree keyform first-half)
,(%case/tree keyform rest-cases)))))))
(let (($keyform (gensym "CASE/TREE-")))
`(let ((,$keyform ,keyform))
,(%case/tree $keyform (sort (copy-list cases) #'< :key #'first))))))
;;;; Threading Macro
(defmacro -<> (expr &rest forms)
"Thread the given forms, with `<>` as a placeholder."
;; I am going to lose my fucking mind if I have to program lisp without
;; a threading macro, but I don't want to add another dep to this library, so
;; here we are.
`(let* ((<> ,expr)
,@(mapcar (lambda (form)
(if (symbolp form)
`(<> (,form <>))
`(<> ,form)))
forms))
<>))