Since ELAN allows the user to define his own syntax by giving a signature
with a mixfix syntax, the syntactic analysis is already complex and it
is not possible to use generators like Lex and
for the fixed part of the syntax which excludes user-defined terms. So
the Earley algorithm is used to analyse the part of programs which depends
on the user-defined syntax for terms, while the other part is analysed
by an automaton generated by a Yacc-like tool.