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Diffstat (limited to 'tutorial')
| -rw-r--r-- | tutorial/list.md | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/tutorial/list.md b/tutorial/list.md index b34587ca..c144a3ac 100644 --- a/tutorial/list.md +++ b/tutorial/list.md @@ -148,15 +148,17 @@ With a left argument `⌽` means Rotate instead, and shifts values over by the s <!--GEN Primitives ⟨"¨%2%Each", "´%5%Fold", "∾%,%Join%Join To"⟩ --> -The 1-modifier Each (`¨`) applies its operand to every element of a list argument, like `map` in a functional programming language. With two list arguments, Each pairs the corresponding elements like arithmetic does, or a bit like a `zip` function (unlike arithmetic, it only goes one level deep). If one argument is a list and one's an atom, the atom is reused every time instead. +The 1-modifier Each (`¨`) applies its operand to every element of a list argument, like `map` in a functional programming language. So here's how we'd reverse each of three lists. ⌽¨ "abcd"‿"ABCDEF"‿"01" - "string"‿"list"‿"array" ∾¨ 's' +Given two list arguments, Each pairs the corresponding elements—first with first, second with second, and so on, like a `zip` function. If just one argument's a list and the other's an atom, it reuses the atom in every pair instead. This many-to-many or one-to-many pairing is the same as we saw for arithmetic. But Each only ever goes one level deep while arithmetic keeps going until it reaches a non-list. + + "abc" ⋈¨ "ABC" - "abc" ⋈¨ ⌽ "abc" + "string"‿"list"‿"array" ∾¨ 's' -Fold (`´`) is the higher-order function also known as reduce or accumulate. It applies its operand function between each pair of elements in a list argument. For example, `+´` gives the sum of a list and `×´` gives its product. +Next, Fold (`´`) is the higher-order function also known as reduce or accumulate. The argument has to be a list, and it applies its operand function between all the elements of that list. For example, `+´` gives the sum of a list and `×´` gives its product. +´ 2‿3‿4 ×´ 2‿3‿4 @@ -166,7 +168,7 @@ To match the order of BQN evaluation, Fold moves over its argument array from ri -´ 1‿2‿3‿4‿5 1-2-3-4-5 -With this evaluation order, `-´` gives the *alternating sum* of its argument. Think of it this way: the left argument of each `-` is a single number, while the right argument is made up of all the numbers to the right subtracted together. So each `-` flips the sign of every number to its right, and every number is negated by all the `-`s to its left. The first number (`1` above) never gets negated, the second is negated once, the third is negated twice, returning it to its original value… the signs alternate. +With this evaluation order, `-´` gives the *alternating sum* of its argument, which comes up in math once in a while. Think of it this way: the left argument of each `-` is a single number, while the right argument is made up of all the numbers to the right subtracted together. So each `-` flips the sign of every number to its right, and every number is negated by all the `-`s to its left. The first number (`1` above) never gets negated, the second is negated once, the third is negated twice, returning it to its original value… the signs alternate. *Hey, isn't it dissonant that the first, second, and third numbers are negated zero, one, and two times? Not if you call them the zeroth, first, and second…* |