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