Reference compiler — executable trace

This trace keeps the program small enough to hold in your head. It lets the compiler show three visible products: a successful check, generated Go source, and program output.

When you set TYPE_RB_TRB, you choose a different local compiler identity. That is useful while developing, but its output matches this pinned clinic only when you built the same revision.

What you need

a trb command on your PATH; and
a Go toolchain, because the trace uses the default Go mode.

You can point the script at another compiler binary with TYPE_RB_TRB.

Run it

From the contributor-guide repository:

./scripts/trace-reference.sh

Read the source

The script prints traces/reference/answer.trb.
Check it

trb check runs parsing, name resolution, and type checking. It does not generate target source.
Generate Go

trb build --stdout runs the complete frontend, lowers the checked program, and asks the Go backend for source. The script shows only the beginning; the complete temporary file is deleted when the trace ends.
Run it

trb run generates, compiles, and starts the program. The final line is:
```
answer=42
```

Connect the output to the map

answer.trb
  -> cmd/trb selects standalone Go mode
  -> compiler parses, resolves, and checks
  -> lower.Program creates typed IR
  -> codegen.Generate emits Go
  -> Go toolchain builds and runs the program

The script cannot print every in-memory compiler value, and that is useful: the normal command-line boundary stays stable while internal structures can improve. Follow the same expression through a few highlighted implementation decisions in the reference code clinic. Use the big map later when you need more source addresses.

Make one safe experiment

Change the return value in answer() from Integer to a string:

return "forty-two"

Run the trace again. It should stop during checking, before Go generation. Read the diagnostic as a compact report of the checker’s job: expected type, actual type, and source location.

The diagnostic guide shows how to trace that failure backward from the visible result without depending on current checker helper names.