From c22b23fb51e6f143019d3b4be3c03a48431d4e5f Mon Sep 17 00:00:00 2001
From: Yogthos <yogthos@gmail.com>
Date: Mon, 15 Jun 2026 15:15:32 -0400
Subject: [PATCH] Reader: #() params survive syntax-quote (auto-gensym names)
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#(...) named its synthesized params with bare gensyms, so a #() written inside a
syntax-quote had its params qualified to the current ns by sq-symbol — and a
qualified symbol isn't a valid fn param. hiccup's compiler emits
`(let [sb# ..] (iterate! #(.append sb# %) ..)), which broke with "Unable to
resolve symbol: ns/_NNNN".

Name the params with a trailing # (auto-gensym suffix, like Clojure's p1__N#) so
syntax-quote maps them consistently and leaves them unqualified. Harmless outside
a backtick (just a regular symbol name).
---
 docs/spec/02-reader.md      | 5 +++++
 src/jolt/reader.janet       | 9 +++++++--
 test/spec/macros-spec.janet | 9 ++++++++-
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/docs/spec/02-reader.md b/docs/spec/02-reader.md
index 0cc7598..6d7fb70 100644
--- a/docs/spec/02-reader.md
+++ b/docs/spec/02-reader.md
@@ -125,6 +125,11 @@ checks → UNVERIFIED (rows to add).
   nested form including vector, map and set literals — `#(assoc {} :k %)`,
   `#(hash-set % %2)` and `#(get {:t %} :t)` all see their `%`s. (A reader that
   scanned only call forms would miscompile `#(identity {:text %})` as a 0-arg fn.)
+- The synthesized parameters are auto-gensyms (their names carry the `#` suffix,
+  like Clojure's `p1__N#`), so an `#()` written inside a syntax-quote survives:
+  the params are mapped consistently and left unqualified rather than being
+  qualified to the current namespace (a qualified symbol is not a valid
+  parameter). E.g. ``  `(map #(inc %) xs) `` expands correctly inside a macro.
 - `#()` literals MUST NOT nest.
 
 ```clojure
diff --git a/src/jolt/reader.janet b/src/jolt/reader.janet
index 46883be..3b61731 100644
--- a/src/jolt/reader.janet
+++ b/src/jolt/reader.janet
@@ -448,10 +448,15 @@
         nil))
     (scan-pct form)
     # One canonical gensym per slot 1..max-n (placeholders for unused), plus rest.
+    # Param names carry a trailing `#` (auto-gensym suffix, matching Clojure's
+    # `p1__N#`) so a #() written inside a syntax-quote survives: sq-symbol treats
+    # `#`-suffixed names as auto-gensyms (mapped consistently, left unqualified)
+    # rather than qualifying them to the current ns — a qualified symbol is not a
+    # valid fn param. Harmless outside a backtick (just a regular symbol name).
     (def slot-syms @{})
     (var i 1)
-    (while (<= i max-n) (put slot-syms i (sym (string (gensym)))) (++ i))
-    (def rest-sym (if has-rest (sym (string (gensym))) nil))
+    (while (<= i max-n) (put slot-syms i (sym (string (gensym) "#"))) (++ i))
+    (def rest-sym (if has-rest (sym (string (gensym) "#")) nil))
     # Pass 2: replace each %-symbol with its slot's gensym.
     (defn- replace-pct [f]
       (cond
diff --git a/test/spec/macros-spec.janet b/test/spec/macros-spec.janet
index eb35387..5dd1fbd 100644
--- a/test/spec/macros-spec.janet
+++ b/test/spec/macros-spec.janet
@@ -24,7 +24,14 @@
   ["gensym unique"      "false"
    "(= (gensym) (gensym))"]
   ["gensym# in template" "true"
-   "(do (defmacro m [] `(let [x# 1] x#)) (= 1 (m)))"])
+   "(do (defmacro m [] `(let [x# 1] x#)) (= 1 (m)))"]
+  # An #() lambda written inside a syntax-quote: its generated params must not be
+  # qualified to the ns (a qualified symbol is not a valid param). hiccup's
+  # compiler emits `(let [sb# ..] (run! #(.append sb# %) ..)) (jolt-nkx).
+  ["#() inside syntax-quote" "[2 4 6]"
+   "(do (defmacro m [] `(mapv #(* % 2) [1 2 3])) (m))"]
+  ["#() + auto-gensym share in template" "\"ab\""
+   "(do (defmacro m [] `(let [sb# (StringBuilder.)] (mapv #(.append sb# %) [\"a\" \"b\"]) (.toString sb#))) (m))"])
 
 # Core macros ported from Janet to the Clojure overlay (jolt-1j0 phase 3,
 # jolt-core/clojure/core/30-macros.clj).