mirror of
https://github.com/janet-lang/janet
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6b95326d7c
remove some complexity and unexpected behavior around numbers in general as all numbers are the same number type, IEEE 754 double precision numbers. Also update examples and tests, some of which were out of date. Some more testing may be needed for new changes to numbers.
107 lines
2.4 KiB
Plaintext
107 lines
2.4 KiB
Plaintext
# An example implementation of functional, lazy
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# sequences, as in clojure. The lazy seq is essentially
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# A lazy linked list, where the next value is a function
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# that must be called (realizing it), and the memoized.
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# Use with (import "./path/to/this/file" :prefix "seq.")
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(defmacro delay
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"Lazily evaluate a series of expressions. Returns a function that
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returns the result of the last expression. Will only evaluate the
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body once, and then memoizes the result."
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[& forms]
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(def state (gensym))
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(def loaded (gensym))
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~(do
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(var ,state nil)
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(var ,loaded nil)
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(fn []
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(if ,loaded
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,state
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(do
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(set ,loaded true)
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(set ,state (do ,;forms)))))))
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# Use tuples instead of structs to save memory
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(def- HEAD 0)
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(def- TAIL 1)
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(defn empty-seq
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"The empty sequence."
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[] nil)
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(defmacro cons
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"Create a new sequence by prepending a value to the original sequence."
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[h t]
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(def x (tuple h t))
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(fn [] x))
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(defn empty?
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"Check if a sequence is empty."
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[s]
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(not (s)))
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(defn head
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"Get the next value of the sequence."
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[s]
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(get (s) HEAD))
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(defn tail
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"Get the rest of a sequence"
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[s]
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(get (s) TAIL))
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(defn lazy-range
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"Return a sequence of integers [start, end)."
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[start end &]
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(if end
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(if (< start end)
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(delay (tuple start (lazy-range (+ 1 start) end)))
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empty-seq)
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(lazy-range 0 start)))
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(defn lazy-map
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"Return a sequence that is the result of applying f to each value in s."
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[f s]
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(delay
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(def x (s))
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(if x (tuple (f (get x HEAD)) (map f (get x TAIL))))))
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(defn realize
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"Force evaluation of a lazy sequence."
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[s]
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(when (s) (realize (tail s))))
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(defn realize-map
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"Evaluate f on each member of the sequence. Forces evaluation."
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[f s]
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(when (s) (f (head s)) (realize-map f (tail s))))
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(defn drop
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"Ignores the first n values of the sequence and returns the rest."
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[n s]
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(delay
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(def x (s))
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(if (and x (pos? n)) ((drop (- n 1) (get x TAIL))))))
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(defn take
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"Returns at most the first n values of s."
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[n s]
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(delay
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(def x (s))
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(if (and x (pos? n))
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(tuple (get x HEAD) (take (- n 1) (get x TAIL))))))
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(defn randseq
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"Return a sequence of random numbers."
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[]
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(delay (tuple (math/random) (randseq))))
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(defn take-while
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"Returns a sequence of values until the predicate is false."
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[pred s]
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(delay
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(def x (s))
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(when x
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(def thehead (get HEAD x))
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(if thehead (tuple thehead (take-while pred (get TAIL x)))))))
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