aowlparser

A pure-nimony recursive-descent parser that turns Nim source into the parse-dialect AIF (.p.aif) the compiler frontend consumes — the same job as the classic compiler's nifler, but self-hosted and free of the classic Nim compiler, so it can be compiled to JavaScript and run in the browser.

Its output is byte-for-byte identical to native nifler — save for one line it owns on purpose, the (.vendor "aowlparser") header (aowlparser stamps its own identity rather than impersonating nifler). The entire nimony source tree and standard library round-trip (184/184 nimony/src byte-exact, 105/105 nimony/lib structural parity), and all 169 corpus programs pass — 154 of them byte-for-byte.

Beyond nimony's own tree, aowlparser is validated against the full upstream Nim standard library by differential fuzzing: all 310 of 310 Nim/lib files now round-trip structure-identical to nifler — 283 of them byte-for-byte — with 0 crashes and 0 hangs. Every construct in the real Nim stdlib parses, including term-rewriting template patterns, Inf/NaN hex-bit literals, custom numeric literals (1'big), method-chain continuations, multi-do calls, and pragma-decorated lambda sugar.

Where aowlparser goes beyond nifler — its diagnostics are built to be a markedly better front end for editors, LSPs, and CI:

• Never dies on the first error. It recovers and keeps parsing, so one run surfaces every problem — and it never cascades into the phantom end-of-file errors a one-shot parser spews once it loses its place. Across the full Nim compiler test corpus, on files where both report errors, nifler emits ~2× the error lines we do.
• Fix-its. Every grammar error carries a suggested repair (help: insert ':', help: did you mean '=='?) — the classic parser has no such concept.
• Related locations. A mismatched bracket points at both the close and the ( it should have matched (note: '(' opened here), as a structured field.
• Machine-readable. --diagnostics:json emits {severity, code, message, line, col, endCol, fix, related} per diagnostic, for editor quick-fixes.
• Full lexer-error parity, and then some. Every classic lexical error nifler reports, aowlparser now reports too, recovering past each instead of aborting: bad character literals (empty '', run-on 'ab', unterminated 'a), illegal tabs (anywhere outside strings/comments), unterminated block comments (#[ … ), malformed escapes (\q, empty \x, empty \u{}), unterminated triple/raw strings, doubled/trailing underscores in a number, and unterminated accent-quoted identifiers.
• Detections nifler lacks or reports vaguely: assignment in a condition (if x = 5: → did you mean ==?), empty conditions (elif:), empty comma slots (foo(a,,b) — while correctly allowing a valid trailing comma), invalid numeric/identifier literals, and full UTF-8 identifier support.
• "Forgot the introducer" family. Where nifler only spits a bare invalid indentation at a stray body line, aowlparser names the actual omission and points at the declaration: a routine with a body but no = (proc f() ⏎ echo 1), a type Name with an indented body but no = object/= enum, and a colon-block whose body isn't indented past its header. Each carries the exact fix-it.
• Precise grammar diagnostics where nifler is terse or cryptic: func used in a type description (→ use proc with {.noSideEffect.}), a keyword where an enum member is expected (when spliced into an enum body), an empty object-variant branch (of A: with no field — we point at the branch itself, not the innocent next one), and an of with no value before its :.
• Knows what isn't plain Nim. A file opening with a #? stdtmpl source-code filter is a template, not Nim — check stays silent instead of flagging the raw HTML, where nifler only tokenizes it by luck.
• Every check is proven zero-false-positive against ~600 valid files and the whole Nim standard library, and never changes the emitted AIF.

Measured against the full Nim compiler test corpus (2890 files): where nifler reports a syntax error, aowlparser now reports one too — except a small residue of indentation-context errors deliberately left out (see below). We report zero false errors on files nifler accepts, and we parse cleanly 6 files that crash nifler outright.

Honest limitation: nifler still flags a handful of subtle indentation-context errors we don't — those are deliberately left out rather than risk a false positive on valid code.

📖 Full docs → aoughwl.github.io/docs/aowlparser

• Architecture — fused parse + emit, the range-splitter, the module map, the oracle
• Grammar coverage — every construct reproduced
• Differential testing — the nifler oracle harness
• Configuration — brace blocks (--curly), indentation/whitespace policy, lint checks, --strict/--max-depth, and stdio I/O
• Known gaps — the honest edge-case catalog

aowlparser p in.nim out.p.aif           # parse Nim source -> nifler-compatible AIF
aowlparser check in.nim                  # lint / report diagnostics, recovering past errors
aowlparser p --diagnostics:json in.nim out.p.aif   # structured diagnostics for tooling

Everything is off by default, so a plain run is byte-compatible with nifler.