09b4e3e1bd
- types.janet: ns? now accepts both structs and tables
(defensive for namespace-like tables created via @{...})
- core.janet: wire comment macro into core-bindings
(was in core-macro-names but missing from core-bindings)
- sci/lang_stubs.clj: minimal SCI type stubs for bootstrap
(IBox, HasName, IVar, DynVar protocols, SciUnbound/Var/Namespace deftypes)
- test-load-sci.janet: load stubs before SCI source files,
removed broken preprocessor
Before: 315 ok, 2 fail (SciVar + array/buffer)
After: 316 ok, 1 fail (only deftype in lang.cljc remains)
The remaining failure is lang.cljc's SciVar deftype with #?@ inserts
for JVM/CLJS-specific protocol implementations — a known limitation
for Phase 15 (SCI bootstrap).
67 lines
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3 KiB
Markdown
67 lines
No EOL
3 KiB
Markdown
---
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name: jolt-gotchas
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description: Common pitfalls and workarounds discovered during Jolt implementation
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---
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# jolt-gotchas
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Recurring pitfalls and their fixes discovered across all implementation phases.
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## PHM/Set Metadata Key Leakage
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PHM and set internal keys (`:jolt/deftype`, `:cnt`, `:buckets`, `:_meta`, `:jolt/type`, `:phm`) leak into `pairs`/`keys` iteration. Must filter in merge, merge-with, keys, vals, and print-collection.
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```janet
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(when (and (not= k :jolt/deftype) (not= k :cnt)
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(not= k :buckets) (not= k :_meta)
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(not= k :jolt/type) (not= k :phm)) ...)
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```
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## Keywords with `#` Are Invalid Janet Literals
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`:#inst`, `:#uuid` cause parse errors. Use dynamic table construction:
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```janet
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(let [dr @{}] (put dr (keyword "#inst") fn) dr)
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```
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## Janet `break` Only Works in Loops
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Does NOT work inside `let`. Use `(var found nil)` + `(set found val) (break)` pattern.
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## Bare Tuples in `eval` Are Function Calls
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`(eval [1 2 3])` calls `1` as function. Use `['tuple 1 2 3]` in data-structure emitter.
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## Janet `case` for Multi-Arity
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Janet lacks Clojure-style multi-arity defn. Use `(defn f [& args] (case (length args) 1 ... 2 ...))`.
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## core-renames + core-fn-values Must Stay in Sync
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Both tables must be updated together when adding core fns. Missing entries = silent nil returns. `"-"` is `core-sub` NOT `core--`.
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## `set!` Field Mutation Reader Quirk
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`(set! (.-x obj) val)` parses as array with `.-x` symbol head — not as standalone `.-x` symbol. Check for this case before the `(. obj -field)` shorthand.
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## Janet `cond` Requires `true` Guard for Catch-All
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A bare expression in the last position of `cond` is treated as a **test** clause (not body). Use `true` as the test:
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```janet
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(cond (nil? x) (buf "nil") (number? x) (buf (string x)) true (buf (string x)))
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```
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Without `true`, the last expression executes as a side-effect test between branches. Hit us in buffer-based write-value — raw tuple addresses leaked into REPL output.
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## REPL: Buffer-Based Output Prevents C-Runtime Interleaving
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Janet's C runtime in `jpm build` executables interleaves native `<tuple 0x...>` output between `prin` statements. Solution: build entire output string in a buffer, then output atomically with a single `print` call. Use `write-value/v buf` + `print-value` creates buffer → `print (string buf)`.
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## Janet `struct?` Returns `true` for Tuples
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Always check `(tuple? x)` BEFORE `(struct? x)` in cond forms. Otherwise `(get tuple :key)` fails with "expected integer key for tuple in range [0, N), got :key". Hit us in `print-value` (symbol check on tuples) and `eval-form` struct handling.
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## PHM Internal Key Leakage
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PHM and set internal keys (`:jolt/deftype`, `:cnt`, `:buckets`, `:_meta`, `:jolt/type`, `:phm`) leak into `pairs`/`keys` iteration. Core fns that iterate collections (`core-merge`, `core-reduce`, `core-every?`, `core-filter`) must check for `set?`/`phm?` first and use type-aware helpers (`phm-to-struct`, `phs-seq`, `phm-keys`, `phm-entries`) before generic iteration. |