From 4e0ff0ac609eb016d14a56e6689d718999e7dd92 Mon Sep 17 00:00:00 2001
From: Robin Jadoul <robin.jadoul@3milabs.tech>
Date: Fri, 6 Feb 2026 13:51:35 +0100
Subject: [PATCH] spec: Introduce array expressions

Closes #135
---
 spec/chip.typ        | 4 ++--
 spec/expr.typ        | 3 +++
 spec/src/branch.toml | 2 +-
 spec/src/shift.toml  | 6 +++---
 spec/tooling/chip.py | 3 +++
 5 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/spec/chip.typ b/spec/chip.typ
index 4749b886e..f3ac28a74 100644
--- a/spec/chip.typ
+++ b/spec/chip.typ
@@ -52,9 +52,9 @@
 #let render_chip_padding_table(chip, config) = {
   // Whether `var` is a preprocessed variable.
   let is_preprocessed(var) = {
-    config.variables.types
+    let type = config.variables.types
     .filter(t => t.label == var.type)
-    .all(t => t.at("preprocessed", default: false))
+    type.len() > 0 and type.all(t => t.at("preprocessed", default: false))
   }
 
   let instantiated_vars = config.variables.categories.instantiated.map(c => chip.variables.at(c, default: ())).flatten()
diff --git a/spec/expr.typ b/spec/expr.typ
index 1c6c7942e..c4f84eb59 100644
--- a/spec/expr.typ
+++ b/spec/expr.typ
@@ -28,6 +28,7 @@
 // <expr> ::= ()                           ; ""
 //          | var                          ; str(var)
 //          | int                          ; int
+//          | ["arr", expr, ...]           ; [expr, ...]
 //          | ["idx", expr1, expr2]        ; expr1[expr2]
 //          | ["not", expr]                ; !expr
 //          | ["+", expr1, expr2, ...]     ; expr1 + expr2 + ...
@@ -91,6 +92,7 @@
 // Typeset an expression as code
 #let expr_to_code = make_expr_formatter(
   (
+    "arr": (pp, rec, e) => `[` + e.slice(1).map(rec.with(PREC.MAX)).join(`, `) + `]`,
     "idx": (pp, rec, e) => rec(PREC.MIN, e.at(1)) + `[` + rec(PREC.MAX, e.at(2)) + `]`,
     "not": (pp, rec, e) => cwrap(rec(PREC.not, 1) + ` - ` + rec(PREC.not, e.at(1)), pp < PREC.not),
     "+": (pp, rec, e) => cwrap(e.slice(1).map(rec.with(PREC.add)).join(` + `), pp < PREC.add),
@@ -149,6 +151,7 @@
 // Typeset an expression as math
 #let expr_to_math = make_expr_formatter(
   (
+    "arr": (pp, rec, e) => $[#e.slice(1).map(rec.with(PREC.MAX)).join($, $)]$,
     "idx": (pp, rec, e) => {
       let (val, idxs) = flat_idxs(e)
       $#rec(PREC.idx, val)_(#idxs.map(idx => rec(PREC.idx, idx)).join($, $))$
diff --git a/spec/src/branch.toml b/spec/src/branch.toml
index beb3c1922..34bcdf8cb 100644
--- a/spec/src/branch.toml
+++ b/spec/src/branch.toml
@@ -34,7 +34,7 @@ pad = 0
 name = "next_pc_high"
 type = ["Half", 3]
 desc = "The upper part of the next pc"
-pad = 0 # TODO(#128): improve handling for arrays
+pad = ["arr", 0, 0, 0]
 
 [[variables.output]]
 name = "next_pc_low"
diff --git a/spec/src/shift.toml b/spec/src/shift.toml
index bd6c471a6..5faed54c7 100644
--- a/spec/src/shift.toml
+++ b/spec/src/shift.toml
@@ -65,19 +65,19 @@ pad = 1
 name = "X"
 type = ["Half", 5]
 desc = "scratch variable."
-pad = 0 # TODO: array
+pad = ["arr", 0, 0, 0, 0, 0]
 
 [[variables.auxiliary]]
 name = "Y"
 type = ["Half", 4]
 desc = "scratch variable."
-pad = 0 # TODO: array
+pad = ["arr", 0, 0, 0, 0]
 
 [[variables.auxiliary]]
 name = "limb_shift"
 type = ["Bit", 4]
 desc = "One-hot vector indicating whether $floor.l #`shift` / 16 floor.r equiv i mod s$, where $s = 2$ when $#`word_instr` = 1$ and $4$ otherwise."
-pad = 0 # TODO: array
+pad = ["arr", 0, 0, 0, 0]
 
 # Virtual
 
diff --git a/spec/tooling/chip.py b/spec/tooling/chip.py
index 8a15ae338..6a78dc091 100644
--- a/spec/tooling/chip.py
+++ b/spec/tooling/chip.py
@@ -62,6 +62,7 @@ def get_const(self) -> int:
 type Expr = (
     LitExpr
     | VarExpr
+    | ArrExpr
     | IdxExpr
     | CastExpr
     | MulExpr
@@ -303,6 +304,8 @@ def build_expr(config: Optional["Config"], data: object) -> Expr:
                 x.isidentifier(), f"Invalid identifier name for variable {x!r}"
             )
             return VarExpr(x)
+        case ["arr", *elems]:
+            return ArrExpr([build_expr(config, e) for e in elems])
         case ["idx", x, y]:
             return IdxExpr(build_expr(config, x), build_expr(config, y))
         case ["cast", x, t]: