Exercise 1 | RACSO

Exercise 1_›:

Expressions over binary +

The set of tokens of the language is {+,NUMBER}. The token NUMBER represents unsigned integers, i.e., non-empty sequences of digits. Recall that “1”, “2+3” and “4+5+6+7” are correct expressions, whereas “+”, “6+” and “1 2” are not. The generated AST must correspond to an interpretation of + as a left-associative operator. For example, for input 1+2+3, the resulting AST must be +(+(1,2),3), i.e., as if the implicit parenthesization was (1+2)+3.

Authors: Carles Creus, Guillem Godoy, Nil Mamano / Documentation:

// In the first problem on parsing we directly propose a solution, in
// order to show which is the syntax to represent the grammars. You
// just have to uncomment (remove //) the following two lines and
// submit:
//
//   exp: NUMBER ('+'^ NUMBER)*;
//   NUMBER: ('0'..'9')+;
//
// Note that symbols enclosed in quotes (' or ") are literal tokens,
// while identifiers started with a lowercase letter denote variables
// and identifiers started with an uppercase letter denote tokens. As
// an alternative solution you can uncomment the following three lines:
//
//   exp: num ('+'^ num)*;
//   num: NUMBER;
//   NUMBER: ('0'..'9')+;
//
// In this case, since exp appears first, it is supposed to be the
// starting variable.
// The available operations are:
//   X | Y : if the lookahead is in the First set of X or if X is
//     nullable and the lookahead is in the Follow set of the whole
//     expression, parse X, otherwise, try to parse Y
//   X* : while the lookahead is in the First set of X, parse X
//   X+ : equivalent to (X X*)
//   X? : equivalent to (X | )
// The available AST construction directives are ^ and !, and must
// appear after a token:
//   ! : the token must not be inserted in the AST
//   ^ : the token must become the root of the current AST
// Finally, in the definition of a token no identifier can be used, the
// AST operators ! and ^ are forbidden, and the following two extra
// operators might be used:
//   .. : denotes a range of characters, like '0'..'9'
//   ~  : denotes the complement of a set of characters, like ~'"' for
//     all non-double-quote characters, or like ~('0'..'9') for all
//     non-digits

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Exercise 1›:

Exercise 1_›: