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Update docstrings in boot.janet (#506)

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Elaborate on usage of reduce and accumulate.
This commit is contained in:
Calvin Rose 2020-11-26 10:32:05 -06:00
parent a3e812b86d
commit 451340e4c0
1 changed files with 13 additions and 6 deletions
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19
src/boot/boot.janet
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@ -811,11 +811,15 @@
(defn reduce
"Reduce, also know as fold-left in many languages, transforms
an indexed type (array, tuple) with a function to produce a value."
an indexed type (array, tuple) with a function to produce a value by applying f to
each element in order. f is a function of 2 arguments, (f accum el), where
accum is the initial value and el is the next value in the indexed type ind.
f returns a value that will be used as accum in the next call to f. reduce
returns the value of the final call to f."
[f init ind]
(var res init)
(each x ind (set res (f res x)))
res)
(var accum init)
(each el ind (set accum (f accum el)))
accum)
(defn reduce2
"The 2-argument version of reduce that does not take an initialization value.
@ -833,7 +837,8 @@
(defn accumulate
"Similar to reduce, but accumulates intermediate values into an array.
The last element in the array is what would be the return value from reduce.
The init value is not added to the array.
The init value is not added to the array (the return value will have the same
number of elements as ind).
Returns a new array."
[f init ind]
(var res init)
@ -842,7 +847,9 @@
ret)
(defn accumulate2
"The 2-argument version of accumulate that does not take an initialization value."
"The 2-argument version of accumulate that does not take an initialization value.
The first value in ind will be added to the array as is, so the length of the
return value will be (length ind)."
[f ind]
(var k (next ind))
(def ret (array/new (length ind)))