The set of tokens of the language is {+,.,IDENT}. The token IDENT represents identifiers. Such tokens are non-empty sequences of alphanumeric characters and underscore, not starting by a digit. Examples of correct expressions are “s.m + x.a”, “x + a.f.m”, “i”, and examples of incorrect expressions are “x.”, “.y.z+w”, “_a+”, “x..y”, etc. The generated AST must correspond to an interpretation of the operator + as left-associative. Field access must be represented by a subtree with the symbol “.” as root, the struct being accessed as first child and the field as second child. Note that the implicit parenthesization of “st.fi.z” is “(st.fi).z”. For instance, the following input x.y.z + i produces the following AST +(.(.(x,y),z),i)