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purepy — Python

Target: Python · Lineage: CoreFn-JSON source-emitter (Jurist architecture) · By: this project (Claude-authored, afc-maintained) · Status: 422/426 differential parity · Repo: in-ecosystem (purescript-backends/purescript-python-new)

purepy borrows Python's ubiquity and data tooling — the inverse argument to most of the family: the libraries are the reason to be there. Rebooted from scratch on the Jurist architecture (ADR-0001), it reached 422/426 byte-identical — the same score as Jurist on the shared corpus.

The one structural twist is module-level lambda lifting (ADR-0002), needed to clear CPython's parenthesis-nesting cap that deeply curried code would otherwise blow.

At a glance

	purepy
Int	Python bignum
Strings	`str` — Unicode codepoints
Architecture	Jurist skeleton + module-level lambda lifting
Build	spago with `backend.cmd: "true"` for CoreFn, then `purepy output output-py`

Divergences

Diverges from JS exactly like the other bignum/UTF-8 backends (INT64 / ASTRAL ledger): Python int is arbitrary precision, so sumTo 1000000 gives the exact answer; float repr differs from JS in the usual zones (inf vs Infinity if unshimmed); ASTRAL- tests agree with Julia and BEAM. Its own test-project/cross_backend_test.py is the prior art for the column-adding task, with a curated KNOWN_DIVERGENCES set worth porting.