Migration demo

The canonical demo migrates a small Python object into JavaScript (and back).

Source (`examples/demo.py`)

state = {
    "username": "Ada",
    "score": 42,
    "projects": ["compiler", "runtime", "vm"],
}
print("python state ready:", state)

Python → JavaScript

plx migrate examples/demo.py --to javascript -o examples/demo.migrated.js

What happens:

Capture — Python worker executes the file and encodes state as PIR
Analyze — semantic-loss pass for JavaScript
Convert — PIR rewritten under the default conversion policy
Restore — JavaScript worker materializes the bindings
Emit — optional JS source preview written to -o

You should see measured timings similar to:

Migration python → javascript (OK)
timings:
  capture: … µs
  analyze: … µs
  convert: … µs
  restore: … µs
  total:   … µs

migrated bindings:
  state: map{3}

Numbers are wall-clock measurements, not placeholders.

Emitted preview (shape):

const state = { "username": "Ada", "score": 42, "projects": ["compiler", "runtime", "vm"] };

JavaScript → Python

plx migrate examples/demo.js --to python -o examples/demo.migrated.py

Integer precision policy

examples/demo_bigint.py uses a value outside the JS safe integer range (9007199254740993).

Flags	Result
(default)	Convert to BigInt (`prefer_bigint=true`) — migration OK, finding `SAFE`
`--no-prefer-bigint`	Rejected as `LOSSY` / `MigrationRejected`
`--no-prefer-bigint --allow-lossy`	Coerce to JS `Number` (opt-in precision loss)

plx migrate examples/demo_bigint.py --to javascript --no-prefer-bigint
# → fails with structured MigrationRejected

plx migrate examples/demo_bigint.py --to javascript -o examples/demo_bigint.migrated.js
# → score becomes 9007199254740993n in the preview

Snapshot along the way

plx migrate examples/demo.py --to javascript \
  --snapshot /tmp/demo.migrated.plx \
  -o /tmp/demo.migrated.js

plx inspect /tmp/demo.migrated.plx

Machine-readable report

plx migrate examples/demo.py --to javascript --json

Includes the migration report (findings + timings) and the migrated PIR bindings object.

Parallax Documentation