Metaprogramming for Loops

[mihaibudiu]

Personnel

• Owner:
• Supporters: @mbudiu-vmw

Design

• Document: see below

Implementation

• p4-spec:
• p4c:

Process

• LDWG discussed:
• LDWG approved:
• Merged into p4-spec:
• Merged into p4c:

Here's an (arguably ugly) way to do statically unrolled loops, but which could be very useful in practice:
Define a new preprocessor macro:

#for i (min, max, step)
body
#endfor i

This is expanded by the preprocessor into:

#define i min
#line original
body
#undef i
#define i (min + step)
#line original
body
...
#undef i
#define i (min + ((max - min) / step) * step)
#line original
body
#undef i

[mihaibudiu]

Related to #84

[mihaibudiu]

Explore uses of boost preprocessor to achieve the same goals.
https://www.boost.org/doc/libs/1_75_0/libs/preprocessor/doc/AppendixA-AnIntroductiontoPreprocessorMetaprogramming.html

[jnfoster]

In the interest of tidying up the set of active issues on the P4 specification repository, I'm marking this as "stalled" and closing it. Of course, we can always re-open it in the future if there is interest in resurrecting it.

Also, we have other issues like #1261 addressing finer-grained proposals.