Fear and Loathing in Parse Vegas

Martin Fowler writes about parser fear and I have to say "guilty as charged". I've done a few DSL but all have be so simple that I could hand-write a parser using regular expressions and other string manipulations. To be honest, the resulting parser would probably be easier to understand, maintain, etc, if it was developed using a proper grammar and a parser generator. Despite (knowing) this, I kept writing those convoluted hand-written parsers.

I did the compiler class at the university and I'm intressted in most things programming langage related, e.g., compilers and parsers. Despite this I never actually done a parser (with proper grammar) by my self. Why? I had parser fear.

Fowler writes:

So why is there an unreasonable fear of writing parsers for DSLs? I think it boils down to two main reasons.

• You didn't do the compiler class at university and therefore think parsers are scary.
• You did do the compiler class at university and are therefore convinced that parsers are scary.

I think the last bullet explains why I never did a proper-grammar-parser by my self.

However, the last time I had to write a parser I (finally) realized that a proper-grammar-parser was a better idea than trying to hand-write something convoluted. The parser should be implemented in Ruby, so I googled (is that a verb now?) and found a generic recursive decent parser -- all I had to do was to write the grammar, which was straight forward.

There were several resons that finally made me take the step to use a proper parser:

• The language was complex enough to make my old approach unsuitable
• The parser was really easy to integrate with my other Ruby code
• No separate step for generating the parser (i.e. short turn-around time, and less complexity because there is no code generation)
  

In essense: it was easy to use and test. That was the cure for my (irrational) anxiety towards parsers.

The Zen of regular expressions

I'm a proud owner, and sometimes wearer, of this (scroll down to Regular Expressions Shirt). On my way home from work today I started to think about whether I really know regular expressions. Sure, I can write expressions that match fairly complex patterns... but do I really know them? I came to the conclusion that I know regexp in the same sense as most seven-year-olds (i.e., first graders) can read and write: they know letter and short words, but not much more.

The funny thing is that if I had been asked this question a few years ago I would have answered of course I know regexps without much thought. Does that mean that I know less about regular expression now than I did then? No, I know more. I now know enough to know that I don't know them.

The Zen of regular expressions:

The first step towards knowing regular expressions is to realize you do not know them.

Since I'm just starting to reach this first step, I cannot tell what the next step will be... or how many steps there are. :)