Don't allow list destructuring with aliases in bqn.js and vm.bqn

3 files changed, 7 insertions, 1 deletions

diff --git a/docs/bqn.js b/docs/bqn.js
index 2ea49108..879859a6 100644
--- a/docs/bqn.js
+++ b/docs/bqn.js
@@ -75,6 +75,8 @@ let set = (d, id, v) => {
     let cs=v.sh.slice(1); let c=cs.reduce((a,b)=>a*b,1);
     let cell = j => arr(v.slice(c*j,c*j+c),cs,v.fill);
     id.map((n,j)=>set(d,n,cell(j)));
+  } else if (id.m) {
+    throw Error("← or ↩: Can't use alias in list destructuring");
   } else {
     if (v.sh) {
       if (!eq(id.sh,v.sh)) throw Error("← or ↩: Target and value shapes don't match");
diff --git a/test/cases/namespace.bqn b/test/cases/namespace.bqn
index d4397fed..421c2e3f 100644
--- a/test/cases/namespace.bqn
+++ b/test/cases/namespace.bqn
@@ -21,6 +21,7 @@
 2  % b←{a⇐𝕩}2⋄⟨b⇐a⟩↩b⋄b
 6  % (d⇐b)‿a←{b⇐1+a⇐𝕩}2⋄a×d
 !  % a2←0⋄⟨a2⇐a⟩+↩{a⇐1}
+!  % ⟨b⇐c,d⟩←1‿2
 
 # Namespaces
 2  % ns←{a⇐2,b⇐3} ⋄ ⟨a⟩←ns ⋄ a
diff --git a/vm.bqn b/vm.bqn
index f00f7fb9..b133cbf7 100644
--- a/vm.bqn
+++ b/vm.bqn
@@ -35,13 +35,15 @@ ref ← {
     Get  ⇐ {𝕩.Get@}¨ arr˙
     # Common code for all setter functions
     # 𝕨S𝕩 sets reference 𝕨 to 𝕩, and e indicates error handling
+    al ← ∨´ {⟨al⟩:al;0}¨ arr
     _set_ ← {S _𝕣_ e:
       Err ← {(e∾": "∾𝕩)!e≡@ ⋄ ⟨1⟩} # e≡@ indicates SetQ, which can't error
       c ← (e≡@) ⊑ {𝔽}‿{𝔽⎊1}        # GetF or Get in F can error
       # Get field for reference 𝕨 from namespace, if possible
       F ← {⟨G⇐GetF⟩𝕊𝕩:(G𝕩).Get@ ; !Err"Cannot extract non-name from namespace"}
       {
-        0=•Type𝕩 ? arr ≡○≢◶⟨Err∘"Target and value shapes don't match", S¨⟩ 𝕩 ;
+        0=•Type𝕩 ? Err⍟al "Can't use alias in list destructuring"
+                   arr ≡○≢◶⟨Err∘"Target and value shapes don't match", S¨⟩ 𝕩 ;
         6=•Type𝕩 ? (⊢ S F⟜𝕩)_c¨ arr ;
         Err "Multiple targets but atomic value"
       }
@@ -64,6 +66,7 @@ ref ← {
   Alias ⇐ {env‿name 𝕊 r:
     SetN‿SetU‿SetQ ⇐ r
     GetF ⇐ {env.program 𝕩.Field name}
+    al ⇐ 1
   }
   # Destructuring placeholder ·
   not ⇐ { SetU⇐SetN⇐⊢ ⋄ SetQ⇐0˙ }