COSC 4400 - Compiler Construction
Spring 2019

Gustave Programming Language

This semester we will be working on a compiler for
a subset of Eiffel.  Eiffel is an object-oriented language
which is particularly known for its support of
"design by contract".  Eiffel is named after the builder
of the Eiffel tower, Gustave Eiffel.  Therefore, our
"little" version of Eiffel will be called Gustave.

A formal grammar for Gustave is attached, as well as
a sample program which uses most of the features in
Gustave.  You can find many tokens in the grammar.
Here is a brief mention of aspects of the language
not apparent from the grammar.

Comments are indicated by two dashes ("--") and extend
to the end of the current line.  Strings are
available for use in output statements (put_string).
There is no string type and no string operations in
Gustave.  String literals are enclosed in double quotes.
There are three special symbols within strings: %" represents
a double quote character, %N represents a newline, and
%% represents a percent character.  For example, the
string The "sale" was 1% off!, with a newline after, would
be written "The %"sale%" was 1%% off!%N" .

Identifiers begin with a letter and can continue with letters,
digits, and underscore ("_").  Within functions, the name
Result is a special variable to hold the return value of the
function.  It is automatically declared to match the function
return type.  I would recommend that the lexeme "Result" be
given its own token (like a keyword).

The convention in Eiffel is that class names consist entirely
of upper-case letters (ACCOUNT rather than Account) and that
constants begin with a capital letter followed by lower-case
(Maxargs rather than MAXARGS).  This is the opposite of the
convention in Java.  Some Eiffel compilers require the class
names to be upper-case.  We won't worry about it in Gustave,
but I will try to always declare class names in upper-case.

Numeric constants consist of an unsigned string of digits (0-9).
Boolean literals are the keywords true and false.