From 58daa8c981f28d6e44e9a894aa524db01214c6a1 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Thu, 9 Dec 2021 18:52:42 +0100
Subject: [PATCH] Drop discards in smart pattern constructors

---
 packages/core/src/runtime/pattern.ts | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/packages/core/src/runtime/pattern.ts b/packages/core/src/runtime/pattern.ts
index 898d4df..8a1a431 100644
--- a/packages/core/src/runtime/pattern.ts
+++ b/packages/core/src/runtime/pattern.ts
@@ -2,7 +2,7 @@
 /// SPDX-FileCopyrightText: Copyright © 2016-2021 Tony Garnock-Jones <tonyg@leastfixedpoint.com>
 
 import { canonicalString, is, KeyedDictionary, Record, RecordConstructorInfo, Value } from '@preserves/core';
-import { AnyValue } from './actor.js';
+import { AnyValue, Ref } from './actor.js';
 import * as P from '../gen/dataspacePatterns.js';
 
 export type Path = Array<AnyValue>;
@@ -164,26 +164,35 @@ export function lit(v: AnyValue): P.Pattern {
     return P.Pattern.DLit(P.DLit(v));
 }
 
+function indexedMembers(items: P.Pattern[]): KeyedDictionary<number, P.Pattern, Ref> {
+    const members = new KeyedDictionary<number, P.Pattern, Ref>();
+    items.forEach((p, i) => {
+        if (!is(p, _)) members.set(i, p);
+    });
+    return members;
+}
+
 export function rec(label: AnyValue, ... fields: P.Pattern[]): P.Pattern {
     return P.Pattern.DCompound(P.DCompound.rec({
         ctor: P.CRec({
             label,
             arity: fields.length,
         }),
-        members: new KeyedDictionary(fields.map((p, i) => [i, p])),
+        members: indexedMembers(fields),
     }));
 }
 
 export function arr(... patterns: P.Pattern[]): P.Pattern {
     return P.Pattern.DCompound(P.DCompound.arr({
         ctor: P.CArr(patterns.length),
-        members: new KeyedDictionary(patterns.map((p, i) => [i, p])),
+        members: indexedMembers(patterns),
     }));
 }
 
 export function dict(... entries: [AnyValue, P.Pattern][]): P.Pattern {
-    return P.Pattern.DCompound(P.DCompound.dict({
-        ctor: P.CDict(),
-        members: new KeyedDictionary(entries),
-    }));
+    const members = new KeyedDictionary<AnyValue, P.Pattern, Ref>();
+    entries.forEach(([k, p]) => {
+        if (!is(p, _)) members.set(k, p);
+    });
+    return P.Pattern.DCompound(P.DCompound.dict({ ctor: P.CDict(), members }));
 }