Editing Eiffel (programming language) (section)

===Lexical and syntax properties===
Eiffel is not case-sensitive. The tokens <code>make</code>, <code>maKe</code> and <code>MAKE</code> all denote the same identifier. See, however, the "style rules" below.

Comments are introduced by <code>--</code> (two consecutive dashes) and extend to the end of the line.

The semicolon, as instruction separator, is optional. Most of the time the semicolon is just omitted, except to separate multiple instructions on a line. This results in less clutter on the program page.

There is no nesting of feature and class declarations. As a result, the structure of an Eiffel class is simple: some class-level clauses (inheritance, invariant) and a succession of feature declarations, all at the same level.

It is customary to group features into separate "feature clauses" for more readability, with a standard set of basic feature tags appearing in a standard order, for example:

<syntaxhighlight lang="eiffel">
class HASH_TABLE [ELEMENT, KEY -> HASHABLE] inherit TABLE [ELEMENT]

    feature -- Initialization
         -- ... Declarations of initialization commands (creation procedures/constructors) ...

    feature -- Access
         -- ... Declarations of non-Boolean queries on the object state, e.g. item ...

    feature -- Status report
         -- ... Declarations of Boolean queries on the object state, e.g. is_empty ...

    feature -- Element change
         -- ... Declarations of commands that change the structure, e.g. put ...

    -- etc.
end
</syntaxhighlight>

In contrast to most [[curly bracket programming language]]s, Eiffel makes a clear distinction between expressions and instructions. This is in line with the [[Command-Query Separation]] principle of the Eiffel method.