WIP draft ranges concept

concepts/ranges/.meta/config.json

@@ -0,0 +1,7 @@
+{
+  "authors": [
+    "colinleach"
+  ],
+  "contributors": [],
+  "blurb": "Ranges in Julia return a lazily-evaluated collection that can be iterated over, or converted to an array."
+}

concepts/ranges/about.md

@@ -0,0 +1,124 @@
+# About
+
+Suppose you want all the non-negative integers up to 1000.
+It would be ridiculous if you had to type these into an array.
+
+For this we have the `range` type:
+
+```julia-repl
+julia> 0:1000
+0:1000
+
+julia> typeof(0:1000)
+UnitRange{Int64}
+```
+
+Ranges are very common: not just to save you typing, but also as return types from functions.
+
+Note that ranges are _not_ arrays.
+
+Arrays are defined at the start ("greedy" evaluation), and need storage proportional to the array length.
+
+In contrast, ranges are just a set of instructions to generate a sequence ("lazy" evaluation, or an "iterator").
+
+If you need a range as an array, use the [`collect()`][collect1] function for conversion:
+
+```julia-repl
+julia> collect(0:5)
+6-element Vector{Int64}:
+ 0
+ 1
+ 2
+ 3
+ 4
+ 5
+```
+
+Optionally, use [`collect(type, range)`][collect2] to specify the output array type.
+
+The step size can be specified, in this case 0.3:
+
+```julia-repl
+julia>  collect(1.0:0.3:2.0)
+4-element Vector{Float64}:
+ 1.0
+ 1.3
+ 1.6
+ 1.9
+```
+
+So the syntax is `start:stepsize:stop`.
+Both end limits are _inclusive_, as seen in the integer example.
+If the step size does not divide exactly into `stop - start`, the last element will avoid exceeding `stop`.
+
+For finer control, use the [`Base.range()` function][base-range], which has several more options.
+
+## Letter ranges
+
+Non-numeric sequences can also be used in ranges.
+The simplest example is [ASCII letters][ascii]:
+
+```julia-repl
+julia> 'a':'d'
+'a':1:'d'
+
+julia> typeof('a':'d')
+StepRange{Char, Int64}
+
+julia> collect('a':'d')
+4-element Vector{Char}:
+ 'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
+ 'b': ASCII/Unicode U+0062 (category Ll: Letter, lowercase)
+ 'c': ASCII/Unicode U+0063 (category Ll: Letter, lowercase)
+ 'd': ASCII/Unicode U+0064 (category Ll: Letter, lowercase)
+```
+
+The `Char` type will be covered in more detail in another Concept.
+For now, just treat these as single characters in single-quotes.
+
+## Functions and operators for ranges
+
+Check the limits of a range with `first()` and `last()`.
+
+Finding whether a particular value is part of a range is often useful.
+The underlying function for this is `in()`, but it is more common to use the infix operator `in` or its more mathematical synonym `∈`.
+In a suitable editor, the shortcut to `∈` is `\in` then tab.
+
+```julia
+ r = 1:10  # => 1:10
+ first(r)  # => 1
+ last(r)   # => 10
+ 7 in r    # => true
+ 11 ∈ r    # => false
+```
+
+The `in` or `∈` operator is used here with ranges, but can also be used with several other collection types such as vectors, sets and dictionaries.
+
+## More on array indexing
+
+Integer ranges and arrays can be used in array indexing:
+
+```julia
+nums = collect(10.0:50.0)
+nums[3:2:7]  # gives [12.0, 14.0, 16.0]
+nums[ [3, 5, 7] ] # also gives [12.0, 14.0, 16.0]
+```
+
+Use with `end` also works, though operator precedence means parentheses may be necessary:
+
+```julia-repl
+ nums[(end - 3):end]
+4-element Vector{Float64}:
+ 47.0
+ 48.0
+ 49.0
+ 50.0
+```
+
+Of course, any of the index elements can be an already-existing integer variable.
+
+
+[base-range]: https://docs.julialang.org/en/v1/base/math/#Base.range
+[ascii]: https://en.wikipedia.org/wiki/ASCII
+[collect1]: https://docs.julialang.org/en/v1/base/collections/#Base.collect-Tuple{Any}
+[collect2]: https://docs.julialang.org/en/v1/base/collections/#Base.collect-Tuple{Type,%20Any}

concepts/ranges/introduction.md

@@ -0,0 +1,90 @@
+# Introduction
+
+Suppose you want all the non-negative integers up to 1000.
+It would be ridiculous if you had to type these into an array.
+
+For this we have the `range` type:
+
+```julia-repl
+julia> 0:1000
+0:1000
+
+julia> typeof(0:1000)
+UnitRange{Int64}
+```
+
+Ranges are very common: not just to save you typing, but also as return types from functions.
+
+Note that ranges are _not_ vectors.
+They are just a set of instructions to generate a sequence ("lazy" evaluation, or an "iterator").
+
+If you need a range as a vector, use the `collect()` function for conversion:
+
+```julia-repl
+julia> collect(0:5)
+6-element Vector{Int64}:
+ 0
+ 1
+ 2
+ 3
+ 4
+ 5
+```
+
+The step size can be specified, in this case 0.3:
+
+```julia-repl
+julia>  collect(1.0:0.3:2.0)
+4-element Vector{Float64}:
+ 1.0
+ 1.3
+ 1.6
+ 1.9
+```
+
+So the syntax is `start:stepsize:stop`.
+Both end limits are _inclusive_, as seen in the integer example.
+If the step size does not divide exactly into `stop - start`, the last element will avoid exceeding `stop`.
+
+## Letter ranges
+
+Non-numeric sequences can also be used in ranges.
+The simplest example is ASCII letters:
+
+```julia-repl
+julia> 'a':'d'
+'a':1:'d'
+
+julia> typeof('a':'d')
+StepRange{Char, Int64}
+
+julia> collect('a':'d')
+4-element Vector{Char}:
+ 'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
+ 'b': ASCII/Unicode U+0062 (category Ll: Letter, lowercase)
+ 'c': ASCII/Unicode U+0063 (category Ll: Letter, lowercase)
+ 'd': ASCII/Unicode U+0064 (category Ll: Letter, lowercase)
+```
+
+The `Char` type will be covered in more detail in another Concept.
+For now, just treat these as single characters in single-quotes.
+
+## Functions and operators for ranges
+
+Check the limits of a range with `first()` and `last()`.
+
+```julia
+ r = 1:10  # => 1:10
+ first(r)  # => 1
+ last(r)   # => 10
+```
+
+## More on vector indexing
+
+Integer ranges and vectors can be used in vector indexing:
+
+```julia
+nums = collect(10.0:50.0)
+nums[3:2:7]  # gives [12.0, 14.0, 16.0]
+nums[ [3, 5, 7] ] # also gives [12.0, 14.0, 16.0]
+```

concepts/ranges/links.json

@@ -0,0 +1,6 @@
+[
+  {
+    "url": "https://docs.julialang.org/en/v1/base/math/#Base.range",
+    "description": "The range() function."
+  }
+]

config.json

@@ -1149,6 +1149,11 @@
       "uuid": "90365822-f58c-4e45-88be-430978b77e65",
       "slug": "numbers",
       "name": "Numbers"
+    },
+    {
+      "uuid": "3ce09c90-3096-4dcc-a53f-66d0054cbe43",
+      "slug": "ranges",
+      "name": "Ranges"
     }
   ],
   "key_features": [