[Basics] new concept (#779)

* New concept basics

* Update concepts/basics/about.md

Co-authored-by: András B Nagy <[email protected]>

* Update concepts/basics/about.md

Co-authored-by: András B Nagy <[email protected]>

* Update concepts/basics/links.json

Co-authored-by: András B Nagy <[email protected]>

* Fix small typo in about.md

* formatting cleanup

* recycled old UUID from unwanted concept

* a few typos and inelegancies fixed

* synced introduction.md with Lasagna exercise

* Update config.json

---------

Co-authored-by: András B Nagy <[email protected]>
Co-authored-by: depial <[email protected]>
Co-authored-by: Colin Leach <[email protected]>

Author: 4 people

concepts/integer-introduction/.meta/config.json renamed to concepts.wip/integer-introduction/.meta/config.json

@@ -0,0 +1,10 @@
+{
+  "authors": [
+    "colinleach"
+  ],
+  "contributors": [
+    "SaschaMann",
+    "cmcaine"
+  ],
+  "blurb": "An introduction to Julia variables, constants and functions."
+}

concepts/integer-introduction/about.md renamed to concepts.wip/integer-introduction/about.md

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+# About
+
+Julia is a dynamic, strongly-typed programming language.
+The programming style is mainly functional, though with more flexibility than in languages such as Haskell.
+
+There is a strong and versatile type system, which will become important in later concepts. 
+In practice, Julia will usually infer a suitable default from the context.
+
+Despite its emphasis on readability, making it appear as a scripting language like Python and Ruby, Julia code is compiled before running.
+The Just In Time (JIT) compiler produces highly optimized code for each function as it is enountered, leading to high runtime speed.
+
+Julia is not an object-oriented language, and there is no class hierarchy of the sort central to many other languages.
+
+Instead *(and please don't panic as you read this!)*, Julia relies on:
+- A *Type* hierarchy.
+- *Composable* functions (designed to combine easily, in versatile and powerful ways).
+- *Multiple dispatch*, meaning functions can be called with variable number and types of arguments.
+
+These rather confusing terms should become clearer as we progress through the syllabus.
+
+The [official documentation][official-documentation] contains a lot of valuable information for the current release, though it can be a bit overwhelming for beginners.
+
+- [Manual][manual]
+- [Tutorials][tutorials]
+- [Get Started with Julia][get-started]
+- [Notes for Python programmers][diff-python]
+- [Notes for R programmers][diff-r]
+- [Notes for C/C++ programmers][diff-c]
+- [Notes for Matlab programmers][diff-matlab] (this is a proprietary language, very popular with engineers and one inspiration for Julia)
+
+Videos include:
+- [A Brief Introduction to Julia][erik] from the Exercism management!
+- [A Gentle Introduction to Julia][gentle-intro]
+- [Learn Julia With Us][learn-with-us] : a 4-part series
+
+## Comments
+
+Including comments in your code is extremely important to help humans read your code and understand your intentions: maybe other people, but also the future you.
+They are (mostly) ignored by the compiler.
+
+Two options are possible in Julia:
+- Single-line comments start with `#`
+- Multi-line comments start with `#=` and end with `=#`. Nesting is allowed.
+
+```julia
+# This is a single-line comment
+
+x = 3  # This is an inline comment
+
+#=
+	Multi-line comments can be used for longer explanations.
+
+	They are especially useful to comment out blocks of code during debugging.
+=#
+```
+
+## Variables and assignment
+
+To create a [variable][variables], just assign a value to it:
+
+```julia-repl
+julia> myvar = 42  # an integer (in fact, Int64)
+42
+
+julia> bigint = 1_234_567_890  # optionally use underscore as digit separator, for readability
+1234567890
+
+julia> name = "Maria"  # strings are surrounded by double-quotes ""
+"Maria"
+```
+
+Assignment ["binds"][binding] a value to the variable.
+
+Specifying a type is optional, and mostly Julia will infer a suitable default from the context.
+
+Types are an important subject in Julia.
+We will explore them further in later concepts.
+For now, it is best not to worry about them.
+
+In contrast to many functional languages, variables in Julia can be reassigned, and you are free to change both the *value* and the *type* bound to the variable:
+
+```julia-repl
+julia> myvar = 3
+3
+
+julia> myvar = "now a string"
+"now a string"
+```
+
+## Constants
+
+Global variables, created outside any function, are:
+- Allowed.
+- Sometimes necessary.
+- Usually discouraged (though only within `*.jl` files; the REPL operates differently).
+
+If a value needs to be available throughout the program, but is not expected to change, use a [constant][constants] instead.
+
+Prefacing the assignemt with the `const` keyword allows the compiler to generate more efficient code.
+
+Accidentally trying to change the `const` value will give a warning:
+
+```julia-repl
+julia> const answer = 42
+42
+
+julia> answer = 24
+WARNING: redefinition of constant Main.answer. This may fail, cause incorrect answers, or produce other errors.
+24
+```
+
+## Arithmetic operators
+
+[Arithmetic][operators] mostly works conventionally:
+
+```julia
+2 + 3  # 5 (addition)
+2 - 3  # -1 (subtraction)
+2 * 3  # 6 (multiplication)
+8 / 2  # 4.0 (division)
+8 % 3  # 2 (remainder)
+2 ^ 3  # 8 (exponentiation)
+```
+
+Note that division with `/` always gives a floating-point value.
+
+We will return to this in later concepts, which will discuss integer division with `div()` or `÷` to truncate and `//` to get a rational number.
+
+## Functions
+
+For best runtime performance, it is best to place most of the code inside [functions][functions]. 
+Having lots of small functions is fine, in contrast to some other languages.
+
+There are two common ways to define a named function in Julia:
+
+1. Using the `function` keyword
+
+    ```julia
+    function muladd(x, y, z)
+        x * y + z
+    end
+    ```
+
+    Indentation by 4 spaces is conventional for readability, but the compiler ignores this.
+    The `end` keyword is essential: more like Ruby than like Python.
+
+    Note that we could have written `return x * y + z`. 
+    However, Julia functions always return the last expression evaluated, so the `return` keyword is optional.
+    Many programmers prefer to include it to make their intentions more explicit.
+
+2. Using the "assignment form"
+
+    ```julia
+    muladd(x, y, z) = x * y + z
+    ```
+
+    This is most commonly used for one-line function definitions or mathematical functions, where the function body is a single expression.
+    A `return` keyword is *never* used in the assignment form.
+
+The two forms are equivalent, and are used in exactly the same way, so choose whichever is more readable.
+
+Invoking a function is done by specifying its name and passing arguments for each of the function's parameters:
+
+```julia
+# invoking a function
+muladd(10, 5, 1)
+
+# and of course you can invoke a function within the body of another function:
+square_plus_one(x) = muladd(x, x, 1)
+```
+
+From the fact that we refer to these as "named" functions, you might guess that there are also "anonymous" functions.
+These will be covered in a later concept.
+
+## Naming conventions
+
+Like many languages, Julia [requires][naming] that names (of variables, functions, and many other things) start with a letter, followed by any combination of letters, digits and underscores.
+
+By convention, variable, constant and function names are *lowercase*, with underscores avoided except when needed to avoid confusion.
+
+However, Julia uses [Unicode][unicode] throughout, so "letter" is interpreted quite flexibly.
+
+Languages other than English are supported, so are emojis *(though please use good taste and pick something appropriate)*.
+
+In particular, all the Greek letters loved by mathematicians are available *(and several useful values are pre-defined)*:
+
+```julia-repl
+julia> π   # a built-in constant
+π = 3.1415926535897...
+```
+
+Julia-aware editors, including the REPL, Pluto.jl, and VS Code with the Julia plugin, make these characters easy to enter.
+
+For π, type `\pi` then hit `<Tab>`. Your typing will be replaced by the Greek character.
+
+You will see many more examples of this in later concepts.
+
+In fact, the backslash-abbreviations are not something specific to Julia.
+They are taken from [LaTeX][latex], a typesetting system that many scientists and engineers use almost daily to write reports.
+
+[official-documentation]: https://docs.julialang.org/en/v1/
+[manual]: https://docs.julialang.org/en/v1/manual/getting-started/
+[tutorials]: https://julialang.org/learning/tutorials/
+[diff-python]: https://docs.julialang.org/en/v1/manual/noteworthy-differences/#Noteworthy-differences-from-Python
+[diff-r]: https://docs.julialang.org/en/v1/manual/noteworthy-differences/#Noteworthy-differences-from-R
+[diff-c]: https://docs.julialang.org/en/v1/manual/noteworthy-differences/#Noteworthy-differences-from-C/C
+[diff-matlab]: https://docs.julialang.org/en/v1/manual/noteworthy-differences/#Noteworthy-differences-from-MATLAB
+[get-started]: https://julialang.org/learning/
+[erik]: https://www.youtube.com/watch?v=X4Alzh3QyWU
+[gentle-intro]: https://www.youtube.com/watch?v=4igzy3bGVkQ
+[learn-with-us]: https://www.youtube.com/watch?v=oTUmW8dWZws
+[variables]: https://docs.julialang.org/en/v1/manual/variables/
+[constants]: https://docs.julialang.org/en/v1/manual/variables-and-scoping/#Constants
+[operators]: https://docs.julialang.org/en/v1/manual/mathematical-operations/
+[functions]: https://docs.julialang.org/en/v1/manual/functions/
+[naming]: https://docs.julialang.org/en/v1/manual/variables/#man-allowed-variable-names
+[unicode]: https://en.wikipedia.org/wiki/Unicode
+[latex]: https://en.wikipedia.org/wiki/LaTeX
+[binding]: https://docs.julialang.org/en/v1/manual/variables/#man-assignment-expressions

concepts/integer-introduction/introduction.md renamed to concepts.wip/integer-introduction/introduction.md

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+# Introduction
+
+The entire Julia track will require you to treat your solution like small libraries, i.e. you need to define functions, types etc. which will then be run against a test suite.
+For that reason, we will introduce named functions as the very first concept.
+
+Julia is a dynamic, strongly-typed programming langauge.
+The programming style is mainly functional, though with more flexibility than in languages such as Haskell.
+
+## Variables and assignment
+
+There is no need to declare a variable in advance.
+Just assign a value to a suitable name:
+
+```julia-repl
+julia> myvar = 42  # an integer
+42
+
+julia> name = "Maria"  # strings are surrounded by double-quotes ""
+"Maria"
+```
+
+## Constants
+
+If a value needs to be available throughout the program, but is not expected to change, it is best to mark it as a constant.
+
+Prefacing an assignment with the `const` keyword allows the compiler to generate more efficient code than is possible for a variable.
+
+Constants also help to protect you against errors in coding.
+Accidentally trying to change the `const` value will give a warning:
+
+```julia-repl
+julia> const answer = 42
+42
+
+julia> answer = 24
+WARNING: redefinition of constant Main.answer. This may fail, cause incorrect answers, or produce other errors.
+24
+```
+
+Note that a `const` can only be declared *outside* any function.
+This will typically be near the top of the `*.jl` file, before the function definitions.
+
+## Arithmetic operators
+
+These are the same as in many other languages:
+
+```julia
+2 + 3  # 5 (addition)
+2 - 3  # -1 (subtraction)
+2 * 3  # 6 (multiplication)
+8 / 2  # 4.0 (division with floating-point result)
+8 % 3  # 2 (remainder)
+```
+
+## Functions
+
+There are two common ways to define a named function in Julia:
+
+1. Using the `function` keyword
+
+    ```julia
+    function muladd(x, y, z)
+        x * y + z
+    end
+    ```
+
+    Indentation by 4 spaces is conventional for readability, but the compiler ignores this.
+    The `end` keyword is essential.
+
+    Note that we could have written `return x * y + z`.
+    However, Julia functions always return the last expression evaluated, so the `return` keyword is optional.
+    Many programmers prefer to include it to make their intentions more explicit.
+
+2. Using the "assignment form"
+
+    ```julia
+    muladd(x, y, z) = x * y + z
+    ```
+
+    This is most commonly used for making concise single-expression functions.
+
+    A `return` keyword is *never* used in the assignment form.
+
+The two forms are equivalent, and are used in exactly the same way, so choose whichever is more readable.
+
+Invoking a function is done by specifying its name and passing arguments for each of the function's parameters:
+
+```julia
+# invoking a function
+muladd(10, 5, 1)
+
+# and of course you can invoke a function within the body of another function:
+square_plus_one(x) = muladd(x, x, 1)
+```
+
+## Naming conventions
+
+Like many languages, Julia requires that names (of variables, functions, and many other things) start with a letter, followed by any combination of letters, digits and underscores.
+
+By convention, variable, constant, and function names are *lowercase*, with underscores kept to a reasonable minimum.

concepts/integer-introduction/links.json renamed to concepts.wip/integer-introduction/links.json

@@ -0,0 +1,18 @@
+[
+  {
+    "url": "https://docs.julialang.org/en/v1/",
+    "description": "Official documentation"
+  },
+  {
+    "url": "https://docs.julialang.org/en/v1/manual/noteworthy-differences/#Noteworthy-differences-from-Python",
+    "description": "Noteworthy Differences from Python"
+  },
+  {
+    "url": "https://www.youtube.com/watch?v=X4Alzh3QyWU",
+    "description": "Exercism: A Brief Introduction to Julia"
+  },
+  {
+    "url": "https://julialang.org/learning/",
+    "description": "Get Started with Julia"
+  }
+]

concepts/basics/.meta/config.json

@@ -1125,6 +1125,11 @@
     ]
   },
   "concepts": [
+    {
+      "uuid": "006ebce8-87cd-4695-87e6-8a7b8dc2f239",
+      "slug": "basics",
+      "name": "Basics"
+    },
     {
       "uuid": "32384ed4-ef26-4118-8ea3-4d44c331e828",
       "slug": "booleans",
@@ -1135,11 +1140,6 @@
       "slug": "vectors",
       "name": "Vectors"
     },
-    {
-      "uuid": "006ebce8-87cd-4695-87e6-8a7b8dc2f239",
-      "slug": "integer-introduction",
-      "name": "Integers and Arithmetic Operations"
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