problem96.ml

(*# P96 (**) Syntax checker (alternative solution with difference lists)
# 
# In a certain programming language (Ada) identifiers are defined by the syntax
# diagram (railroad chart) opposite. Transform the syntax diagram into a system
# of syntax diagrams which do not contain loops; i.e. which are purely
# recursive. Using these modified diagrams, write a predicate identifier/1 that
# can check whether or not a given string is a legal identifier.
# 
# % identifier(Str) :- Str is a legal identifier*)