HACKER Q&A
📣 scotty79

Easiest way to code AST transformations


When writing macros the main idea is to convert the tree that represents the code into a modified tree.

What is the best way to describe such alterations in non ad-hoc, more declarative manner?

The only thing that comes to my mind is something with a functionality of XSLT.

Do you know of some more light weight libraries in any language with similar capabilities as XSLT when it comes to transforming trees into other trees?

  👤 sargstuff Accepted Answer ✓
So, outlining the problem with the provided information:

1) Use gui interface to "draw" a grammer diagram describing the AST/modified

   tree (aka transition diagram / BNF / EBNF / w3 grammer specificatation(s)

   XSLT to use isn't in original request. XSLT grammer for "gui" is version dependent.  

   w3 specification(s) http://www.w3.org  Note:  things other XSLT too! 

   Example program(s) for the 'gui' edit: 

   https://tikzit.github.io/index.html or https://latex-cookbook.net/graph/

   Perhaps bootup a livecd (https://www.tug.org/texlive)
   or online https://www.overleaf.com/
   Use tikzi library from github or graph.tex from latex-cookbook
2) Take latex drawing & transform to lex/yacc description.

   https://github.com/rajnitish/Latex-to-Html-Lex-Yacc/blob/master/parser
3) Rust grmtools, https://softdevteam.github.io/grmtools/master/book has relevant libraries/tools to make use of files generated in step 2.

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Automation idea: No programmer history/preferences for OS/language/environment specified.

So, shell script to "automate"/glue this all togehter as one command line program left as a reader exercise. ;)

👤 gus_massa
Have you read about macros in Scheme/Racket? For example, with define-syntax-rule you can define a rule to transform code that looks like code.

  (define-syntax-rule (repeat3 body ...)
    (begin
      body
      body
      body))
and you just use it

  (repeat3 (print "Hello!"))
expands to

  (begin
    (print "Hello!")
    (print "Hello!")
    (print "Hello!"))
and the output is

  Hello!Hello!Hello!
👤 billconan
I need to simplify parse tree into an AST tree, I'm building a gui tool for drawing state machines, which will be translated to rust code that can do the job,