From d2673317a8dda3619d2e5e489ce13513ff655532 Mon Sep 17 00:00:00 2001
From: Roman Volosatovs <rvolosatovs@riseup.net>
Date: Thu, 27 Aug 2026 18:02:29 +0200
Subject: [PATCH] define map and fixed-length list value encoding

Signed-off-by: Roman Volosatovs <rvolosatovs@riseup.net>
---
 design/mvp/Binary.md    |  3 +++
 design/mvp/Explainer.md | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/design/mvp/Binary.md b/design/mvp/Binary.md
index 3915bb75..7f15ef92 100644
--- a/design/mvp/Binary.md
+++ b/design/mvp/Binary.md
@@ -472,6 +472,7 @@ val(i:<typeidx>)           ::= v:<val(type-index-space[i])>            => v
 val((record (field l t)+)) ::= v+:<val(t)>+                            => (record v+)
 val((variant (case l t?)+) ::= i:<core:u32> v?:<val(t[i])>?            => (variant l[i] v?)
 val((list t))              ::= v:vec(<val(t)>)                         => (list v)
+val((list t len))          ::= (v:<val(t)>)^len                        => (list v^len) 🔧
 val((tuple t+))            ::= v+:<val(t)>+                            => (tuple v+)
 val((flags l+))            ::= (v:<core:byte>)^N                       => (flags (l[i] for i in 0..|l+|-1 if v[floor(i / 8)] & 2^(i mod 8) > 0)) (where N = ceil(|l+| / 8))
 val((enum l+))             ::= i:<core:u32>                            => (enum l[i])
@@ -485,6 +486,8 @@ val((result (error u)))    ::= 0x00                                    => ok
                              | 0x01 v:<val(u)>                         => (error v)
 val((result t (error u)))  ::= 0x00 v:<val(t)>                         => (ok v)
                              | 0x01 v:<val(u)>                         => (error v)
+val((map k v))             ::= e*:vec(<entryval(k, v)>)                => (map e*) 🗺️
+entryval(k, v)             ::= key:<val(k)> val:<val(v)>               => (entry key val) 🗺️
 ```
 
 Notes:
diff --git a/design/mvp/Explainer.md b/design/mvp/Explainer.md
index 3cab3bb2..76ad01b7 100644
--- a/design/mvp/Explainer.md
+++ b/design/mvp/Explainer.md
@@ -2431,7 +2431,9 @@ val      ::= false | true
            | (enum <labellit>)
            | none | (some <val>)
            | ok | (ok <val>) | error | (error <val>)
+           | (map <entryval>*) 🗺️
            | (binary <core:datastring>)
+entryval ::= (entry <val> <val>) 🗺️
 f64canon ::= <core:f64> without the `nan:0x` case.
 ```
 
@@ -2478,6 +2480,17 @@ For example:
   (value $t bool (binary "\00"))
   (value $u string (binary "\07example"))
 
+  ;; 🔧 fixed-length list:
+  (value $v (list u8 3) (list 1 2 3))
+
+  ;; 🗺️ map:
+  (value $w (map string u16)
+    (map
+      (entry "a" 1)
+      (entry "b" 2)
+    )
+  )
+
   (type $complex
     (tuple
       (record