Compilation strategy

[H. S. Teoh]

On Tue, Dec 18, 2012 at 09:55:57AM -0800, Walter Bright wrote:
> On 12/18/2012 9:42 AM, H. S. Teoh wrote:
> >I was thinking more along the lines of things like fully automatic
> >purity, safety, exception inference. For example, every function body
> >eventually has to be processed by the compiler, so if a particular
> >function is inferred to throw exception X, for example, then when its
> >callers are compiled, this fact can be propagated to them. To do this
> >for the whole program might be infeasible due to the sheer size of
> >things, but if a module contains, for each function exposed by the
> >API, a list of all thrown exceptions, then when the module is
> >imported this information is available up-front and can be propagated
> >further up the call chain. Same thing goes with purity and @safe.
> >
> >This may even allow us to make pure/@safe/nothrow fully automated so
> >that you don't have to explicitly state them (except when you want
> >the compiler to verify that what you wrote is actually pure, safe,
> >etc.).
> 
> The trouble with this is the separate compilation model. If the
> attributes are not in the function signature, then the function
> implementation can change without recompiling the user of that
> function. Changing the inferred attributes then will subtly break
> your build.

And here's a reason for using an intermediate format (whether it's
bytecote or just plain serialized AST or something else, is irrelevant).
Say we put the precompiled module in a zip file of some sort.  If the
function attributes change, so does the zip file. So if proper make
dependencies are setup, this will automatically trigger the
recompilation of whoever uses the module.


> Inferred attributes only work when the implementation source is
> guaranteed to be available, such as with template functions.
> 
> Having a binary format doesn't change this.

Actually, this doesn't depend on the format being binary. You can save
everything in plain text format and it will still work. In fact, there
might be reasons to want a text format instead of binary, since then one
could look at the compiler output to find out what the inferred
attributes of a particular declaration are without needing to add
compiler querying features.


T

-- 
Why have vacation when you can work?? -- EC