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NilPy: file I/O (with open), list comprehensions, and dict literals-in-args

Hangs off [[feature-nilpy-corpus-uforth]]. uforth's wall as of 2026-07-20 is line 1228, and it is a CLUSTER, not a single feature — three things land on consecutive lines:

with open(abs_path, "r", encoding="utf-8") as f:
    lines = [raw.rstrip("\n") for raw in f]          # comprehension + file iter
source_id = self._alloc_fileid(
    {"kind": "source", "path": abs_path, "lines": lines}   # dict literal as arg
)

The pieces, roughly in dependency order

  1. with statement — a context manager. For open, the only censused use, this desugars to: open, run the body, close on every exit path (including exceptions). One site, so a narrow with open(...) as f: form is enough; the general protocol (__enter__/__exit__) is not needed yet.
  2. A file object — open(path, mode, encoding=...), iterable BY LINE (for raw in f), plus .read(). This is the real work: a PAL/RTL file primitive plus an iterator that yields lines. sys.stdin (filed separately) needs the same object, so build it once.
  3. List comprehensions — [expr for x in it], and with a filter ([expr for x in it if cond]). 4 sites. Desugars to a fresh TPyList built by a loop; the loop machinery already exists (PyParseForIn), so this is mostly a new expression form that emits an accumulate.
  4. A dict/set literal as a call ARGUMENT — f({...}). Literals work in assignment position; this needs them accepted in an argument position too. Likely small.

Smaller items still past this (census in uforth.py)

Gate

Each piece lands green independently with a CPython-diffed .npy case + --tier quick + self-host byte-identical + make fpc-check clean. The file object in particular needs a test that reads a real temp file and matches CPython line for line.

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