From 7c4671d98fe0cc593ca26c040054a25620f67aa2 Mon Sep 17 00:00:00 2001 From: Calvin Rose Date: Sat, 29 Dec 2018 17:42:44 -0500 Subject: [PATCH] Update loop documentation. --- doc/Loop.md | 34 ++++++++++++++++++++++++++++++---- 1 file changed, 30 insertions(+), 4 deletions(-) diff --git a/doc/Loop.md b/doc/Loop.md index 0c9de3b8..85a5f76e 100644 --- a/doc/Loop.md +++ b/doc/Loop.md @@ -2,13 +2,13 @@ A very common and essential operation in all programming is looping. Most languages support looping of some kind, either with explicit loops or recursion. -Janet supports both recursion and a primitve `while` loop. While recursion is +Janet supports both recursion and a primitive `while` loop. While recursion is useful in many cases, sometimes is more convenient to use a explicit loop to iterate over a collection like an array. ## An Example - Iterating a Range -Supose you want to calculate the sum of the first 10 natural numbers +Suppose you want to calculate the sum of the first 10 natural numbers 0 through 9. There are many ways to carry out this explicit calculation even with taking shortcuts. A succinct way in janet is @@ -16,7 +16,7 @@ even with taking shortcuts. A succinct way in janet is (+ ;(range 10)) ``` -We will limit ourselves however to using explicit looping and no funcitions +We will limit ourselves however to using explicit looping and no functions like `(range n)` which generate a list of natural numbers for us. For our first version, we will use only the while macro to iterate, similar @@ -143,6 +143,32 @@ As before, we can evaluate this loop using only a while loop and the `next` func (set key (next alphabook key)) ``` -For ou +However, we can do better than this with the loop macro using the `:pairs` or `:keys` verbs. +``` +(loop [[letter word] :pairs alphabook] + (print letter " is for " word)) +``` +Using the `:keys` verb and the dot syntax for indexing + +``` +(loop [letter :keys alphabook] + (print letter " is for " alphabook.letter)) +``` + +The symbol `alphabook.letter` is shorthand for `(get alphabook letter)`. +Note that the dot syntax of `alphabook.letter` is different than in many languages. In C or +ALGOL like languages, it is more akin to the indexing operator, and would be written `alphabook[letter]`. +The `.` character is part of the symbol and is recognized by the compiler. + +We can also use the core library functions `keys` and `pairs` to get arrays of the keys and +pairs respectively of the alphabook. + +``` +(loop [[letter word] :in (pairs alphabook)] + (print letter " is for " word)) + +(loop [letter :in (keys alphabook)] + (print letter " is for " alphabook.letter)) +```