Support timer AFTER input (tim ? AFTER expr)

[associate-1]

Difficulty: Medium — Parser, AST, and codegen changes across timer input handling.

Summary

Occam's tim ? AFTER expr construct waits until the timer value exceeds expr. This is used for timed delays and is distinct from tim ? t (which just reads the current time).

Occam syntax

TIMER tim:
INT t:
SEQ
  tim ? t              -- read current time
  tim ? AFTER t PLUS delay  -- wait until time passes t + delay

Proposed Go mapping

t = time.Now().UnixMicro()
time.Sleep(time.Duration(t + delay - time.Now().UnixMicro()) * time.Microsecond)

Or possibly using AFTER comparison semantics (modular time comparison).

Affected files

• bar.occ (lines 176, 189, 225, 373)
• demo.occ (line 16)
• sort_inside_2.occ (line 323)

Work required

1. Parser: Detect AFTER keyword after ? in channel/timer input and parse the delay expression
2. AST: Add an AfterExpr field (or similar) to the input node
3. Codegen: Generate time.Sleep(...) or equivalent

Part of #43.