add names/index.md (#32398)

Notes on names that begin with an upper case letter and those that don't and naming conventions.

guide/english/erlang/names/index.md

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+---
+title: Names
+---
+
+## Names
+
+All programming languages have conventions concerning names.
+Erlang is no different but some of these conventions are, in fact, part of the language.
+
+#### More Information:
+<!-- Please add any articles you think might be helpful to read before writing the article -->
+
+  * [Learn You Some Erlang: Invariable variables](https://learnyousomeerlang.com/starting-out-for-real#invariable-variables)
+  * [Learn You Some Erlang: Atoms](https://learnyousomeerlang.com/starting-out-for-real#atoms)
+  * [Erlang Reference Manual: Preprocessor](http://erlang.org/doc/reference_manual/macros.html)
+  * [Unicode Implementation](http://erlang.org/doc/apps/stdlib/unicode_usage.html#unicode-implementation)
+
+### Names in Erlang
+
+In Erlang, the names of 'variables' begin with an upper case letter
+(which is not how variables are named in most other languages).
+
+Other primitives have names that start with a lower case letter:
+
+  * atoms
+  * functions
+
+There are also preprocessor macros.
+When used in code, their names are preceded by a ?:
+
+```erlang
+    -define(SPACE, $\s).
+
+    without_spaces(String) ->
+        [C || C <- String, C /= ?SPACE].
+```
+
+Macro names are generally all upper case but this is not a requirement.
+
+The underscore may appear in names.
+Erlang programmers favour 'snake case' over 'camel case'.
+
+By convention a leading underscore indicates a placeholder:
+a variable whose value is not going to be used.
+However, it has a value and this is immutable as with other variables.
+
+Except for a single '_'.  This too is a placeholder but
+it will match anything and cannot be bound to a value.
+It may, therefore, be used as often as necessary.
+
+Atoms are names whose value is the name.
+Few programming languages have atoms or anything equivalent.
+
+Atoms may be enclosed in apostrophes (as in 'true' and 'false').
+They may contains spaces, in which case the name must be enclosed in apostrophes.
+
+Do not confuse these with _strings_, which are enclosed in quotes:
+
+```erlang
+    1> 'Hello World' /= "Hello World".
+    true
+```
+
+Erlang has 30 or so 'reserved' words and a larger number of built-in-functions (BIFs)
+whose names all begin with a lower case letter.
+Do not attempt to use these names for your own functions.
+
+Erlang functions are first class.
+A consequence of this is variables can be bound to functions (including, and especially, lambda functions)
+just as they can be bound to numbers.
+
+It will look like the variable is being called as if it where a function.
+Indeed is it but this can be confusing.
+
+Erlang documentation recommends functions that do the same thing in different modules have the same name.
+This is not polymorphism.
+
+Programming languages do not impose conventions on the names of functions.
+Programmer cabals usually do.
+
+Many conventions recommend "meaningful" names.
+Bear in mind that with a programming languages with 'pure functions' and no side-effects,
+it makes more sense to name functions by what they return rather than what they do.
+
+Erlang encourages short functions, which, in turn, allows for shorter descriptions.
+If you find you need impossibly long names for your functions,
+consider splitting them into smaller ones.
+
+### Unicode names in Erlang
+
+Finally a note on Unicode.
+
+Erlang pre-dates Unicode and, as with many other languages,
+used to use ISO Latin-1 through out.
+Unicode support has been added over a number of releases.
+
+Erlang uses UTF8 (not UTF16).
+
+Since Erlang/OTP 17.0, Erlang source files are by default encoded in Unicode.
+
+Since Erlang/OTP 20.0, names of atoms, functions and variables may contain (alphabetic) Unicode characters.
+However, module (and application and node) names must still be ISO Latin-1.
+
+<!-- EOF -->