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351 lines
11 KiB
Plaintext
351 lines
11 KiB
Plaintext
(defmodule Dynamic
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(doc cxr "takes a specification of a traversal in `a` (head) and `d` (tail)
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symbols and a list `pair` to traverse.
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Example:
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```
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(cxr '(1 a 1 d) '(1 2 3)) ; => 2
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(cxr '(1 a 1 d 1 a 4 d) '(1 2 3 4 (5 6 7))) ; => 6
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```")
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(defndynamic cxr [x pair]
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(cond
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(= (length x) 0) pair
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(= 0 (car x)) (cxr (cddr x) pair)
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((cond
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(= 'a (cadr x)) car
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(= 'd (cadr x)) cdr
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(macro-error "`cxr` expects either `a` or `d` symbols, got " (cadr x)))
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(if (= 1 (car x))
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(cxr (cddr x) pair)
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(cxr (cons (- (car x) 1) (cdr x)) pair)))))
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(doc nthcdr "takes the `n`th tail or `cdr` of the list `pair`.")
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(defndynamic nthcdr [n pair]
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(cxr (list (+ n 1) 'd) pair))
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(doc nthcar "takes the `n`th head or `car` of the list `pair`.")
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(defndynamic nthcar [n pair]
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(cxr (list 1 'a n 'd) pair))
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(hidden collect-into-internal)
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(defndynamic collect-into-internal [xs acc f]
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(if (= 0 (length xs))
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acc
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(collect-into-internal (cdr xs) (append acc (f (car xs))) f)))
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(doc collect-into
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"Transforms a dynamic data literal into another, preserving order")
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(defndynamic collect-into [xs f]
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(collect-into-internal xs (f) f))
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(doc empty?
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"Returns true if the provided data literal is empty, false otherwise.")
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(defndynamic empty? [xs]
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(= 0 (length xs)))
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(doc reduce
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"Reduces or 'folds' a data literal, such as a list or array, into a single"
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"value through successive applications of `f`.")
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(defndynamic reduce [f x xs]
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(if (empty? xs)
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x
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(reduce f (f x (car xs)) (cdr xs))))
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(hidden unreduce-internal)
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(defndynamic unreduce-internal [f x lim acc counter]
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;; Currently only works with anonymous functions and named functions.
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;; does not work with commands.
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(if (not (or (array? acc) (list? acc)))
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(macro-error
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"Unreduce requires a dynamic data structure to collect results, such as
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(list) or (array).")
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(if (= counter lim)
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acc
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(unreduce-internal f (f x) lim (append acc (cons (eval (f x)) (empty acc))) (+ counter 1)))))
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(doc unreduce
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"Applies `f` to a starting value `x`, then generates a sequence of values"
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"by successively applying `f` to the result `lim-1` times."
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"Collects results in the structure given by `acc`."
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""
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"```"
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"(unreduce (curry + 1) 0 10 (list))"
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"=> (1 2 3 4 5 6 7 8 9 10)"
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"```")
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(defndynamic unreduce [f x lim acc]
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(unreduce-internal f x lim acc 0))
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(doc filter
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"Returns a list containing only the elements of `xs` that satisify"
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"predicate `p`."
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""
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"```"
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"(filter (fn [x] (= 'a x)) '(a b a b a b a b))"
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"=> (a a a a)"
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"```")
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(defndynamic filter [p xs]
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(let [filter-fn (fn [x y] (if (p y) (append x (list y)) x))]
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(reduce filter-fn (list) xs)))
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(doc reverse
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"Reverses the order of elements in an array or list."
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""
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"```"
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"(reverse [1 2 3 4])"
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"=> [4 3 2 1]"
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"```")
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(defndynamic reverse [xs]
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(if (array? xs)
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(reduce (flip append) (array) (map array xs))
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(reduce (flip append) (list) (map list xs))))
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(doc empty
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"Returns the empty form of `xs`."
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""
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"```"
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"(empty '(1 2 3 4))"
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"=> ()"
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"(empty '[1 2 3 4])"
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"=> []"
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"```")
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(defndynamic empty [xs]
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(if (array? xs)
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(array)
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(list)))
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(doc take
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"Returns a list containing the first `n` elements of a list."
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""
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"```"
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"(take 3 '(1 2 3 4 5))"
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"=> (1 2 3)"
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"```")
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(defndynamic take [n xs]
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;; A more straightforward impl is likely more efficient?
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(let [indicies (unreduce (curry + 1) 0 n (list))
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result (map cadr (zip list xs indicies))]
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(if (array? xs)
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(collect-into result array)
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result)))
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(doc apply
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"Applies the function `f` to the provided argument list, passing each value"
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"in the list as an argument to the function.")
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(defndynamic apply [f argument-list]
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;; The let clause here is a tad mysterious at first glance. When passed a
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;; standalone function name (i.e. not an application (f x), carp evaluates
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;; it into the function's defining form, e.g. foo becomes (defn foo [x] x),
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;; commands such as + become (command +) etc. ;; The binding here accounts
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;; for that case, allowing users to pass the function name to apply
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;; unquoted.
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;;
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;; This is necessary for parity across map-internal, zip, and apply.
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;; Since map calls its function directly, it takes it as is. Apply, on the
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;; other hand, would have to take the quoted form, since it builds a list
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;; that serves as the actual application.
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;;
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;; This is problematic for the user facing map function, since it makes
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;; calls to map or zip (which uses apply) as appropriate--unless we support
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;; the quoted function name argument in map-internal or the unquoted one in
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;; apply, we can't use zip and map-internal in map.
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(if (not (list? f))
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(f argument-list)
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(let [function-name (list (cadr f))]
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(if (array? argument-list)
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(append function-name (collect-into argument-list list))
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(append function-name argument-list)))))
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(doc any?
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"Checks whether any of the elements in `xs` conforms to the predicate"
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"function `f`."
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""
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"```"
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"(any? (fn [x] (= 'a x)) '(a b c))"
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"=> true"
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"(any? (fn [x] (= 'a x)) '(e f g))"
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"=> false"
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"```")
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(defndynamic any? [f xs]
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(reduce (fn [acc x] (or acc (f x))) false xs))
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(doc all?
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"Checks whether all of the elements in `xs` conform to the predicate"
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"function `f`."
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""
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"```"
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"(all? (fn [x] (< 1 x)) '(2 3 4))"
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"=> true"
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"(all? (fn [x] (< 1 x)) '(-1 0 1))"
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"=> false"
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"```")
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(defndynamic all? [f xs]
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(reduce (fn [acc x] (and acc (f x))) true xs))
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(hidden zip-internal)
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(defndynamic zip-internal [f forms acc]
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(if (any? empty? forms)
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acc
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(zip-internal
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f
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(map-internal cdr forms (list))
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(let [result (list (apply f (map-internal car forms (list))))]
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(append acc result)))))
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(doc zip
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"Returns the *form* that results from applying a function `f` to each of"
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"the values supplied in `forms`."
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"If the members of a single form are exhuasted, the result of the"
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"applications thus far is returned, and any remaining members in the other"
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"forms are ignored."
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""
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"```"
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"(zip + '(1 2 3) '(4 5 6))"
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"=> ((+ 1 4) (+ 2 5) (+ 3 6))"
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"```"
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""
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"It's important to note that zip operates on forms, and that the form"
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"returned by zip may not be evaluable by itself. For instance, to actually"
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"transform the result in the example above into something Carp can"
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"evaluate, we need to wrap each member of the list in a `do`:"
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""
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"```"
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"(append (list 'do) (zip + '(1 2 3) '(4 5 6)))"
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"=> (do (+ 1 4) (+ 2 5) (+ 3 6))"
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"(eval (append (list 'do) (zip + '(1 2 3) '(4 5 6))))"
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"=> 9 ;; do returns the value of the last form in its body"
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"```")
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(defndynamic zip [f :rest forms]
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(zip-internal f forms (list)))
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(doc map
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"Applies a function `f` to each element in the list or array `xs` and"
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"returns a list dynamic data literal containing the result of the function"
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"applications."
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""
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"```"
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"'(map symbol? '(a b c))"
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"=> (true true true)"
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"'(map (curry + 1) '(1 2 3))"
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"=> (2 3 4)"
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"```")
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(defndynamic map [f xs]
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(map-internal f xs (list)))
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(doc flatten
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"Flattens a list recursively."
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""
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"```"
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"(flatten '(1 2 (3 (4))))"
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"=> '(1 2 3 4)"
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"```")
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(defndynamic flatten [l]
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(reduce (fn [acc x]
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(if (list? x)
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(append acc (flatten x))
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(cons-last x acc)))
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'()
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l))
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(doc walk "traverses `form`, an arbitrary data structure, using the functions
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`inner` and `outer`. It will apply `inner` to each element of `form`, building
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up a data structure of the same type, then applies `outer` to the result. It
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recognizes arrays and lists. Other data structures will just be passed to
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`outer`.
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Example:
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```
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(walk car reverse [[1 2] [3 4] [5 6]]) ; => [5 3 1]
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```")
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(defndynamic walk [inner outer form]
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(cond
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(list? form) (outer (map inner form))
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(array? form) (outer (collect-into (map inner form) array))
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(outer form)))
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(doc postwalk "Performs a depth-first, post-order traversal of `form` and
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calls `f` on each subform, collecting the result.
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Example:
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```
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; note: this could be achieved using `walk-replace` as well
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(postwalk (fn [x]
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(cond
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(= x '+) '*
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(= x '-) '/
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x))
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'(+ 1 (- 2 3))) ; => (* 1 (/ 2 3))
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```")
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(defndynamic postwalk [f form]
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(walk (curry postwalk f) f form))
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(doc prewalk "behaves like [`postwalk`](#postwalk), but does pre-order
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traversal.
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Example:
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```
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(prewalk (fn [x] (if (number? x) (* x 4) x)) '(+ 1 (- 2 3))) ; => (+ 4 (- 8 12))
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```")
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(defndynamic prewalk [f form]
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(walk (curry prewalk f) (fn [x] x) (f form)))
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(hidden walk-replace-finder)
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(defndynamic walk-replace-finder [p el]
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(if (empty? p)
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p
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(let [f (car p)]
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(if (= (car f) el)
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f
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(walk-replace-finder (cdr p) el)))))
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(doc walk-replace "Performs a depth-first, pre-order traversal of `form` and
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finds a matching replacement for each subform in the replacement pairs `pairs`,
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if applicable, collecting the result.
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Example:
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```
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(walk-replace '((+ *) (- /)) '(+ 1 (- 2 3))) ; => (* 1 (/ 2 3))
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```")
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(defndynamic walk-replace [pairs form]
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(prewalk (fn [x]
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(let [r (walk-replace-finder pairs x)]
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(if (empty? r) x (cadr r))))
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form))
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(defmodule List
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(doc pairs "makes a list of pairs out of a list `l`. If the number of
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elements is uneven, the trailing element will be discarded.")
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(defndynamic pairs [l]
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(if (< (length l) 2)
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'()
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(cons `(%(car l) %(cadr l)) (List.pairs (cddr l)))))
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(doc nth "gets the nth element of the list `l`.")
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(defndynamic nth [l n]
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(cond
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(empty? l) '()
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(= n 0) (car l)
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(List.nth (cdr l) (dec n))))
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(doc update-nth "updates the nth element of the list `l` using the function `f`.")
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(defndynamic update-nth [l n f]
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(cond
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(empty? l) '()
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(= n 0) (cons (f (car l)) (cdr l))
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(cons (car l) (List.update-nth (cdr l) (dec n) f))))
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(doc set-nth "sets the nth element of the list `l` to the value `v`.")
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(defndynamic set-nth [l n elem]
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(List.update-nth l n (fn [_] elem)))
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(doc find "finds the first element in the list `l` that matches `pred`.")
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(defndynamic find [l pred]
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(cond
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(empty? l) '()
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(pred (car l)) (car l)
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(List.find (cdr l) pred)))
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)
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)
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