Implement push command

HELP.md

@@ -314,6 +314,10 @@ Example: Say `$a` is `[1, 2, 3]` and subject is `[a, b, c]` -> `zip $a` -> `[a,
 Collapse a nested destructured string down a single level, optionally limiting to a specific `index`.
 Example: `[[a,b], c, [d,e]]` -> `flatten 2` -> `[[a,b], c, d, e]`
 
+#### `push <value>`
+Append the given `value` to the current destructured.
+Example: `[foo, bar]` -> `push foo` -> `[foo, bar, foo]`
+
 
 ### Working with Variables
 

editor-support/vim/syntax/str.vim

@@ -11,7 +11,7 @@ syn keyword strKeyword exit paste copy infile outfile assign clear show undo red
 syn keyword strKeyword enclose lower upper lsub rsub prefix suffix quote unquote replace rev trim indent concat
 syn keyword strKeyword line word each on drop take missing lines words split chunk join sort unique zip flatten group
 syn match   strKeyword "\<contains\>"
-syn keyword strKeyword to from set over call lipsum convert if unless while table
+syn keyword strKeyword to from set over call lipsum convert if unless while table push
 
 " Types
 syn match strType "::\s*\zs\(string\|int\|destructured\)"

src/vm/commands/index.ts

@@ -59,6 +59,7 @@ import {Unless} from "./unless.js";
 import {Convert} from "./convert.js";
 import {While} from "./while.js";
 import {Table} from "./table.js";
+import {Push} from "./push.js";
 
 export type Commands = Command<CommandData>[]
 export const commands: Commands = [
@@ -96,6 +97,7 @@ export const commands: Commands = [
     new Over,
     new Paste,
     new Prefix,
+    new Push,
     new Quote,
     new Redo,
     new Replace,

src/vm/commands/push.ts

@@ -0,0 +1,32 @@
+import {Command, ParseContext, StrTerm} from "./command.js";
+import {LexInput} from "../lexer.js";
+import {StrVM} from "../vm.js";
+
+export type PushData = {
+    val: StrTerm,
+}
+
+export class Push extends Command<PushData> {
+    async attemptParse(context: ParseContext): Promise<PushData> {
+        return {
+            val: await context.popTerm(),
+        }
+    }
+
+    getDisplayName(): string {
+        return 'push'
+    }
+
+    isParseCandidate(token: LexInput): boolean {
+        return this.isKeyword(token, 'push')
+    }
+
+    async execute(vm: StrVM, data: PushData): Promise<StrVM> {
+        return vm.replaceContextMatchingTerm(ctx => ({
+            destructured: parts => [
+                ...parts,
+                { value: ctx.resolveRequired(data.val) },
+            ],
+        }))
+    }
+}