Editing Interpreter (computing) (section)

=== Abstract syntax tree interpreters ===
{{main|Abstract syntax tree}}
In the spectrum between interpreting and compiling, another approach is to transform the source code into an optimized abstract syntax tree (AST), then execute the program following this tree structure, or use it to generate native code [[Just-in-time compilation|just-in-time]].<ref>[http://lambda-the-ultimate.org/node/716 AST intermediate representations], Lambda the Ultimate forum</ref> In this approach, each sentence needs to be parsed just once. As an advantage over bytecode, the AST keeps the global program structure and relations between statements (which is lost in a bytecode representation), and when compressed provides a more compact representation.<ref name="KistlerFranz1999">{{cite journal
|last1=Kistler |first1=Thomas
|last2=Franz |first2=Michael |author-link2=Michael Franz
|title=A Tree-Based Alternative to Java Byte-Codes
|journal=International Journal of Parallel Programming
|volume=27 |issue=1
|date=February 1999
|pages=21–33
|issn=0885-7458
|doi=10.1023/A:1018740018601
|s2cid=14330985
|citeseerx=10.1.1.87.2257
|url=http://oberon2005.oberoncore.ru/paper/mf1997a.pdf
|access-date=2020-12-20
}}</ref> Thus, using AST has been proposed as a better intermediate format for just-in-time compilers than bytecode. Also, it allows the system to perform better analysis during runtime.

However, for interpreters, an AST causes more overhead than a bytecode interpreter, because of nodes related to syntax performing no useful work, of a less sequential representation (requiring traversal of more pointers) and of overhead visiting the tree.<ref>[http://webkit.org/blog/189/announcing-squirrelfish/ Surfin' Safari - Blog Archive » Announcing SquirrelFish]. Webkit.org (2008-06-02). Retrieved on 2013-08-10.</ref>