Janet Exercism: Implement map

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Blog 2020/8/5

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Janet Exercism: Implement map

Here are Janet solutions (recursive and iterative) to the exercism "implement map without using map" problem.

For some reason, the exercism folks call this problem "accumulate".

Makefile

test-all: mymap-iter mymap-recur mymap-iter.janet mymap-recur.janet
	chmod +x mymap-recur.janet mymap-iter.janet
	./mymap-recur.janet
	./mymap-recur
	./mymap-iter.janet
	./mymap-iter

mymap-iter: mymap-iter.janet
	jpm quickbin mymap-iter.janet mymap-iter

mymap-recur: mymap-recur.janet
	jpm quickbin mymap-recur.janet mymap-recur

clean:
	rm -f mymap-recur mymap-iter mymap-recur.c mymap-iter.c

.PHONY: clean test-all

mymap-iter.janet

#!/usr/bin/env janet

(defn mymap-iter [f arr]
  (var arr2 @[])
  (each x arr
    (array/push arr2 (f x)))
  arr2)

(defn square [x]
  (* x x))

(defn main [& args]
  (pp (mymap-iter square [1 2 3]))
  (pp (mymap-iter square [])))

mymap-recur.janet

#!/usr/bin/env janet

# conceptually, what we want is this:
# (defn mymap [f arr]
#  (join (f (head arr)) (mymap f (tail arr))))

(defn mymap-recur [f arr]
  (if (= 0 (length arr))
    []
    (tuple (f (first arr)) (splice (mymap-recur f (slice arr 1))))))

(defn square [x]
  (* x x))

(defn main [& args]
  (pp (mymap-recur square [1 2 3]))
  (pp (mymap-recur square [])))

Recursion with an index, some sort of middle ground.

(defn map-into [f a ind &opt from]
  (default from 0)
  (if (>= from (length ind))
    a
    (do
      (array/push a (f (in ind from)))
      (map-into f a ind (inc from)))))

(defn map [f ind]
  (map-into f @[] ind))

(pp (map inc [1 2 3]))

@andrewchambers nice!