Building AST's for RPAL Programs Programming Language Principles Lecture 9 Prepared by Manuel E. Bermúdez, Ph.D. Associate Professor University of Florida

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 Programming Language Principles Lecture 9 Prepared by Manuel E. Bermúdez, Ph.D. Associate Professor University of Florida