jolt/.dirge/skills/jolt-bootstrap/SKILL.md

jolt-bootstrap

TDD workflow for bootstrapping a Clojure interpreter on Janet

Bootstrapping a Clojure interpreter on Janet

Prerequisites

• Janet ≥ 1.36, jpm
• Target Clojure sources (e.g. sci) to load
• Jolt sources in src/jolt/, tests in test/

TDD Loop

1. Write a failing test in test/<feature>-test.janet using (use ../src/jolt/...) relative paths
2. Run with janet test/<file>.janet (faster than jpm test for iteration)
3. If test involves init (which loads clojure.core), also (use ../src/jolt/api)
4. Implement in src/jolt/<module>.janet
5. Run test → see failure message → fix → repeat
6. After passing: jpm test to ensure no regressions

Current bootstrap progress

All files parse cleanly. Eval status:

File	Forms	Eval OK	Failures
sci.impl.macros	4/4	4	0
sci.impl.protocols	15/17	15	2 (resolution stubs)
sci.impl.utils	39/47	39	8 (multi-arity, missing deps)
sci.impl.types	22/27	22	5 (resolution stubs)
sci.impl.unrestrict	2/2	2	0
sci.impl.vars	28/28	28	0
sci.lang	10/10	10	0
sci.ctx-store	6/6	6	0
sci.impl.namespaces	93/98	93	5 (missing copy-core-var dep)
sci.core	60/69	60	4 (*1/*2/*3/*e unresolved)

Loading order: macros → protocols → types → unrestrict → vars(27/28, skip comment block) → lang → utils → ctx-store → namespaces → core

Added special forms: quote, syntax-quote, unquote, unquote-splicing, do, if, def, defmacro, fn*, let*, loop*, recur, throw, try, set!, var, locking, instance?, defmulti, defmethod, deftype, new, . (22 total)

Core additions: when (macro), defn (macro with docstring), declare (macro), fn (macro — wraps fn*), Object (interop stub), derive, isa?, ancestors, descendants (hierarchy stubs), defprotocol (macro), extend-type, extend-protocol (macro), extend (macro), reify, satisfies?, extends?, implements?, type->str, comment (macro), prefer-method (stub), unchecked-math (false), clojure-version ({:major 1 :minor 11})

Reader: #?(:clj ...), #?@(:clj ...) with splicing, #_ discard, #\ var-quote, ^ metadata, ; comments → skip, nil #?(:cljs ...) → skip (non-splicing), empty #?@(:cljs ...) → empty splice, unmatched )]} → explicit errors

Current blockers

1. sci.impl.copy-vars not yet loaded — needed for copy-core-var, copy-var, macrofy, new-var
2. sci.impl.resolve, sci.impl.cljs, sci.impl.multimethods, sci.impl.deftype not yet loaded
3. Multi-arity function dispatch edge cases in utils (forms 36-37, 44-45)
4. ~9 remaining eval failures across namespaces (5) and sci.core (4) — all tracing back to missing deps

Key patterns

Symbol structs

{:jolt/type :symbol :ns <string-or-nil> :name <string>}

Macro intern marks var

(def v (ns-intern ns name macro-fn))
(put v :macro true)

Reader conditional #?

Resolves at read time: scans for :clj keyword, picks next form. #?@ wraps resolved form in :jolt/splice struct for list/vec/set splicing. Nil results (e.g. #?(:cljs X) on CLJ) now return {:jolt/type :jolt/skip} for non-splicing and {:jolt/type :jolt/splice :items @[]} for splicing — preventing orphaned keys in maps.

Callable forms check

(if (function? f)
  (apply f args)
  (get f (first args)))  ; table/struct lookup

unwrap-meta-name helper

Recursively unwraps (with-meta sym meta) to extract the underlying symbol. Used in def, ns, deftype, defmethod to handle metadata-wrapped names.

deftype →TypeName constructor

deftype interns both TypeName and ->TypeName (Clojure arrow constructor convention).

Pitfalls

• Janet let can't bind to nil; use (var x nil) then (set x val)
• (get table) with 1 arg = compile error, use (table :key) shorthand
• (put fn :key val) fails on functions; stash metadata on vars instead
• deftype field names must be keywords (not strings) for (inst :field) access
• defn placed after core-bindings that reference it → compile error; order matters
• Janet's try macro: (try body ([err] handler)) — catch clause is tuple [binding body...]
• core-macro-names is a zero-arg fn returning a table: (get (core-macro-names) name). Don't call it as (core-macro-names name) — that's arity mismatch
• Janet #{} sets can cause parse issues — use @[] instead for stub collections
• break in while doesn't return a value in Janet — use (var done nil) + (while (and cond (not done)) ... (set done result)) pattern instead
• (last string) returns nil — last works only on indexed types. Use (s (- (length s) 1)) for last char of string
• (set [a b] tuple) doesn't work — Janet's set doesn't support destructuring. Use (tuple 0) / (tuple 1)
• #_ discard works in lists, vectors, sets, and maps — wraps skipped form in {:jolt/type :jolt/skip} and readers check for this
• Map reader must handle :jolt/skip and :jolt/splice in both key and value positions
• comment macro must be registered in core-macro-names to avoid evaluating its body