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Abstract Syntax Trees

Parsing

ProgrammingLanguages

LispMacros

• http://en.wikipedia.org/wiki/Abstract_syntax_tree
  • Each node of the tree denotes a construct occurring in the source code. The syntax is abstract in the sense that it does not represent every detail that appears in the real syntax. For instance, grouping parentheses is implicit in the tree structure, and a syntactic construct such as if cond then expr may be denoted by a single node with two branches.
• http://en.wikipedia.org/wiki/Concrete_syntax_tree aka Parse Tree
  
  
• http://www.absoluteastronomy.com/encyclopedia/a/ab/abstract_syntax_tree.htm
• What's the difference between a parse tree and an abstract syntax tree (AST)?
  • A parse tree is a record of the rules (and tokens) used to match some input text whereas a syntax tree records the structure of the input and is insensitive to the grammar that produced it.

 AST:
 -------

 +
 | \  
 3  4


 PT:
 -------

 expr
  |
 plus
  | \  \  
  3  +  4