Language Philosophy

Structural vs. Procedural

In traditional programming, if is a procedural control-flow instruction. It tells the compiler to execute code lines sequentially based on a condition. In HDLs, however, the structure is always meant to describe hardware, not a sequence of CPU instructions.

vctx is structural

The keyword when emphasizes that you are defining a condition under which a path exists in the final hardware structure (a multiplexer or priority encoder). It emphasizes the structural selection rather than the procedural execution order. It’s a statement about the circuit’s configuration, not its execution sequence.

Explicit Timing

By defining the roles of assignment operators so clearly, vctx eliminates the major sources of confusion found in older HDLs (like Verilog’s blocking vs. non-blocking assignments).

The <= operator inherently means sequential/clocked. The := operator inherently means combinational/immediate.

This makes the timing intent of your design explicit and readable.