On Thursday, 23 January 2014 at 08:12:08 UTC, OP wrote:
I'd like Walter to reply to this. In his article here
http://www.drdobbs.com/architecture-and-design/so-you-want-to-write-your-own-language/240165488
Walter says
Somewhat more controversial, I wouldn't bother wasting time
with lexer or parser generators and other so-called "compiler
compilers." They're a waste of time. Writing a lexer and
parser is a tiny percentage of the job of writing a compiler.
Using a generator will take up about as much time as writing
one by hand, and it will marry you to the generator (which
matters when porting the compiler to a new platform). And
generators also have the unfortunate reputation of emitting
lousy error messages.
Using bison I can write complex statements which are easy for
me to grok and change. I wouldn't know how to change complex
statements if I hand wrote the parser. I don't know all the
places something like that would affect. Taking the syntax
below I'm not sure how to fork a state and discard the invalid
one.
foo[5] = var2
foo[5] foo = var2
Here when I see foo[5] I'm either accessing an array (first
statement) or declaring variables as an array of 5 elements
(second statement). Just like `Foo&foo` could be a reference or
could be an AND statement. Foo is definitely processed on its
own, I don't know how to process it as both (a fork) and
continue on the parser to find a valid path.
A simple solution to this problem would be to try and parse the
longer statement first. If that doesn't work, then go for the
shorter one. In your first case you have two possible
declarations:
- the 'variable definition': [Type] [Name] ('=' [R-Expression])?
- the 'value assignment'. [L-Expression] '=' [R-Expression]
When you can't parse a variable definition, try the value
definition.
I found that writing a parser in general is not that hard. The
difficult part is figuring out what the syntax and the AST should
look like. I recommend just trying to create something for a
limited set of your language and work your way up from there.
