Builders And Lowering

The compiler uses builder-style structures while lowering and assembling internal representations.

The exact implementation has evolved, but the important idea is stable:

• resolution, elaboration, monomorphization, and lowering each own different responsibilities
• temporary builder state should support those responsibilities without smearing semantics across phases

What Builder State Usually Holds

Builder/lowering state commonly tracks things like:

• symbol/name mappings
• current module/function context
• current Self type or impl context
• temporary locals/register mappings
• transient structures needed only during lowering

Why This Matters

Concrete’s roadmap strongly prefers:

• explicit pass ownership
• fewer hidden cross-phase assumptions
• fewer “special cases because the builder happened to know something”

That is why so much work has gone into clarifying pass contracts, lowering boundaries, and semantic language items.

Modern Direction

The important modern direction is not the exact historical builder shape. It is:

• Resolve owns name resolution
• Check / Elab / CoreCheck own semantics
• Mono owns monomorphization
• Lower owns semantic-to-SSA lowering
• SSAVerify and SSACleanup defend the backend boundary

For the current stable view, prefer:

• docs/ARCHITECTURE.md
• docs/PASSES.md