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Parsers are easy. It's the grammars that are complicated. Seriously: seemingly simple things designed and described informally, in prose, can easily be incredi

by tikhonj 11y ago

Parsers are easy. It's the grammars that are complicated. Seriously: seemingly simple things designed and described informally, in prose, can easily be incredibly complex when you expand all their details. That says a lot about those things, a little bit about the process and mindset that went into them and virtually nothing about parsing in general.

haberman 11y ago
> Parsers are easy. It's the grammars that are complicated. What is this supposed to mean? It sounds something like "Programming is easy. It's the classes/objects that are complicated."
- tikhonj 11y ago
  What I'm saying is that parsing is not inherently hard. But, just like anything else that isn't inherently hard, you can make it as hard as you like by making the input arbitrarily complex and convoluted. Given a grammar, making a parser is largely trivial. A computer could do it. Making a fast parser, or one with good error messages, or one that's modular and composable are all harder, but still generally not hard. The problem comes up when you have a bad, overly complex, ill-thought-out, incomplete or vague specification. But anything would be hard with a specification like that, not just parsing. (This feels like something standards bodies seem to enjoy producing though.) Perhaps it's a bit like saying "programming is easy, the world is complicated" except that the world could be so much less complicated if relevant formal languages were simpler and better-defined.
  - haberman 11y ago
    > The problem comes up when you have a bad, overly complex, ill-thought-out, incomplete or vague specification. But anything would be hard with a specification like that, not just parsing. Nearly nearly every real text format in the world would fall under your definition of "bad, overly complex, ill-thought-out", thanks to practical considerations always leading to some amount of complexity. You may wish that languages could be nice and clean, but in practice they rarely end up that way. But aside from that, your statement isn't true. Serialization is an order of magnitude easier than parsing, because for a serializer all you have to do is emit something that stays within the lines delimited by the spec. For a parser, you have to correctly and safely handle absolutely any construct or variation allowed by the spec.

by tikhonj 11y ago

haberman 11y ago

> Parsers are easy. It's the grammars that are complicated. What is this supposed to mean? It sounds something like "Programming is easy. It's the classes/objects that are complicated."

tikhonj 11y ago
What I'm saying is that parsing is not inherently hard. But, just like anything else that isn't inherently hard, you can make it as hard as you like by making the input arbitrarily complex and convoluted. Given a grammar, making a parser is largely trivial. A computer could do it. Making a fast parser, or one with good error messages, or one that's modular and composable are all harder, but still generally not hard. The problem comes up when you have a bad, overly complex, ill-thought-out, incomplete or vague specification. But anything would be hard with a specification like that, not just parsing. (This feels like something standards bodies seem to enjoy producing though.) Perhaps it's a bit like saying "programming is easy, the world is complicated" except that the world could be so much less complicated if relevant formal languages were simpler and better-defined.
- haberman 11y ago
  > The problem comes up when you have a bad, overly complex, ill-thought-out, incomplete or vague specification. But anything would be hard with a specification like that, not just parsing. Nearly nearly every real text format in the world would fall under your definition of "bad, overly complex, ill-thought-out", thanks to practical considerations always leading to some amount of complexity. You may wish that languages could be nice and clean, but in practice they rarely end up that way. But aside from that, your statement isn't true. Serialization is an order of magnitude easier than parsing, because for a serializer all you have to do is emit something that stays within the lines delimited by the spec. For a parser, you have to correctly and safely handle absolutely any construct or variation allowed by the spec.