[prototyping] Action parameter types and directionality annotations

[chkim4142]

Require types on action parameters
○ Parameters have directionality
■ in: May not be modified, can be a constant or other non-L-value
■ out: May be modified, implied to be uninitialized
■ inout: May be modified, already initialized with data
○ Use syntax similar to header field declaration

action foo (inout header ipv4_t ipv4, in bit<32> new_dst_addr)
{
modify_field(ipv4.dstAddr, new_dst_addr);
}

[ChrisDodd]

On Mon, Oct 19, 2015 at 1:14 PM, chkim4142 notifications@github.com wrote:

action foo (inout header ipv4_t ipv4, in bit<32> new_dst_addr)
{
modify_field(ipv4.dstAddr, new_dst_addr);
}

This example hits the API problem with actions that we're trying to defer
or simplify -- when are action parameters things that need to be set in the
P4 program (in the control flow when the table is applied), and when are
they things that become part of the control plane API (parameters to the
table entry you are installing in a table.)

In v1.0 the action params are always part of the control plane API (so 'in'
only) -- anything that is related to a header or metadata field has to be
bound directly to that field's global name and not passed as a parameter.

[chkim4142]

P4_16 has this.