Studying the DMD front-end and contributing to similar projects?

[Walter Bright]

Aziz K. wrote:
> Hi,
> 
> The specs are not always helpful when you need to know how to write a 
> compiler for D programs.
> 
> Is it okay to study the code of the front-end of DMD, and also 
> contribute to similar projects under a different license?
> 
> What are the restrictions in this regard?

It is under GPL and the Artistic License. If you wish to use it under the GPL, 
the usual GPL conventions apply. If you wish to use it for commercial non-GPL 
purposes, ask me and I will do my best to make it work for you.

I use the compiler source in my Compiler Construction Seminar 
(http://www.astoriseminar.com). So yes, you are free to study the code, learn 
from it, apply the techniques in your own projects, and contribute to other 
projects under a different license.

As far as I know, none of the algorithms used in the compiler are encumbered by 
any patents, certainly I hold no patents on it, nor do I intend to patent any 
part of it. Furthermore, the algorithms used in it are pretty conventional 
compiler algorithms that have been around a long time.

All I ask is that you do not copy the actual source code code without a license 
from Digital Mars or unless the copy is under the GPL.

In particular, I am not requiring anyone to do a clean room implementation. My 
often stated ideas about 'taint' are simply an easy way to protect myself (and 
Digital Mars) against frivolous lawsuits, I have no intention of applying them 
in reverse.

For an example of what doesn't work for me, many years ago, a company came out 
with a product suspiciously similar to mine. I contacted them, and they said 
that while they were familiar with my code, they had rewritten it from scratch. 
Ok, so I ran an "nm" over their executable and a "strings". Of the hundreds 
internal function names (not interface related), about 95% were identical 
matches to my source code, and about 90% of the text strings, such as error 
messages, were identical. This was as obvious and egregious as it gets. They 
were full of BS, and they caved.