Building AST's for RPAL Programs

Prepared by

Manuel E. Bermúdez, Ph.D.Associate ProfessorUniversity of Florida

Programming Language ConceptsLecture 14

Let's Build a Few Abstract Syntax Trees

• Example 1: Factorial, version 3.

• Example 2: Palindrome.

• Example 3: Add numbers from list.

• Example 5: Build tuple of pairs of characters.

Class Project

• Build a recursive descent parser for RPAL (gulp!)

• If done properly, it's easy.• Need lexical analyzer, to be called

repeatedly (important!) by the parser. Avoid scanning the entire input in advance of the parser.

Class Project (cont’d)

• Code up one procedure per nonterminal in RPAL's grammar.

• Pseudo code for some portions of RPAL’s grammar

Class Project (cont’d)

• Implement support module for trees, and stack of trees.• Suggestion: use first-child, next-

sibling binary tree representation of n-ary trees (it works!).

• Preorder traversal of this tree is the same as for n-ary tree.

• Popping n trees from the stack, and building a parent node on top of them, is easy.

Building AST's for RPAL Programs

Prepared by

Manuel E. Bermúdez, Ph.D.Associate ProfessorUniversity of Florida

Programming Language ConceptsLecture 14