36 lines
1.6 KiB
Markdown
36 lines
1.6 KiB
Markdown
|
---
|
||
|
|
layout: news
|
||
|
|
author: Torsten
|
||
|
|
---
|
||
|
|
|
||
|
|
Parsing is a difficult, the theory incomprehensible and older tools cryptic. At least for me.
|
||
|
|
|
||
|
|
And then i heard recursive is easy and used by even llvm. Formalised as peg parsing libraries exists, and in ruby
|
||
|
|
they have dsl's and are suddenly quite understandable.
|
||
|
|
|
||
|
|
Off the candidates i had first very positive experiences with treetop. Upon continuing i found the code
|
||
|
|
generation aspect not just clumbsy (after all you can define methods in ruby), but also to interfere unneccessarily
|
||
|
|
with code control. On top of that conversion into an AST was not easy.
|
||
|
|
|
||
|
|
After looking around i found Parslet, which pretty much removes all those issues. Namely
|
||
|
|
|
||
|
|
- It does not generate code, it generates methods. And has a nice dsl.
|
||
|
|
- It transforms to ruby basic types and has the notion on a transormation.
|
||
|
|
So an easy and clean way to create an AST
|
||
|
|
- One can use ruby modules to partition a larger parser
|
||
|
|
- Minimal dependencies (one file).
|
||
|
|
- Active use and development.
|
||
|
|
|
||
|
|
So i was sold, and i got up to speed quite quickly. But i also found out how fiddly such a parser is in regards
|
||
|
|
to ordering and whitespace.
|
||
|
|
|
||
|
|
I spent some time to make quite a solid test framework, testing the differnet rules seperately and also the
|
||
|
|
stages seperately, so things would not break accidentally when growing.
|
||
|
|
|
||
|
|
After about another 2 weeks i was able to parse functions, both calls and definitions, ifs and whiles and off course basic
|
||
|
|
types of integers and strings.
|
||
|
|
|
||
|
|
With the great operator support it was a breeze to create all 15 ish binary operators. Even Array and Hash constant
|
||
|
|
definition was very quick. All in all surprisingly painless, thanks to Kasper!
|
||
|
|
|