JSON Expressoin "push" operator

src/json-expression/__tests__/jsonExpressionUnitTests.ts

@@ -1640,6 +1640,44 @@ export const jsonExpressionUnitTests = (
       });
     });
 
+    describe('push', () => {
+      test('can push static values into static array', () => {
+        const arr: unknown[] = [];
+        check(['push', [arr], 1], [1]);
+        check(['push', [arr], 1, 2, 3], [1, 2, 3]);
+        check(['push', [arr], 1, '2', true, [[]]], [1, '2', true, []]);
+        check(['push', [[1]], 2, 3], [1, 2, 3]);
+      });
+
+      test('can push static values into array', () => {
+        check(['push', ['$', '/arr'], 1], [1], {arr: []});
+        check(['push', ['$', '/arr'], 1, 2, 3], [1, 2, 3], {arr: []});
+        check(['push', ['$', '/arr'], 1, 2, 3], [0, 1, 2, 3], {arr: [0]});
+      });
+
+      test('can push values into static array', () => {
+        check(['push', [[]], ['$', '/val'], 1], [0, 1], {val: 0});
+      });
+
+      test('can push values into array', () => {
+        check(['push', ['$', '/arr'], ['$', '/val'], '2'], [0, 1, '2'], {arr: [0], val: 1});
+      });
+
+      test('concatenates empty arrays', () => {
+        check(['push', [[1]], [[]]], [1, []]);
+        check(['push', [[]], [[]]], [[]]);
+      });
+
+      test('throws on invalid operand count', () => {
+        expect(() => check(['push', [[]]] as any, false)).toThrowErrorMatchingInlineSnapshot(
+          `""push" operator expects at least two operands."`,
+        );
+        expect(() => check(['push', []] as any, false)).toThrowErrorMatchingInlineSnapshot(
+          `""push" operator expects at least two operands."`,
+        );
+      });
+    });
+
     describe('head', () => {
       test('returns first two elements', () => {
         check(['head', [[1, 2, 3]], 2], [1, 2]);

src/json-expression/codegen.ts

@@ -73,6 +73,7 @@ export class JsonExpressionCodegen {
         link: this.linkOperandDeps,
         const: this.operatorConst,
         subExpression: this.subExpression,
+        var: (value: string) => this.codegen.var(value),
       };
       return codegen(ctx);
     }

src/json-expression/index.ts

@@ -1,3 +1,4 @@
 export * from './types';
 export * from './evaluate';
 export * from './codegen';
+export * from './Vars';

src/json-expression/operators/array.ts

@@ -3,6 +3,7 @@ import {Expression, ExpressionResult, Literal} from '../codegen-steps';
 import {$$deepEqual} from '../../json-equal/$$deepEqual';
 import type * as types from '../types';
 import {Vars} from '../Vars';
+import {clone} from '../../json-clone';
 
 const createSubExpressionOperator = <N extends string>(
   name: N,
@@ -51,6 +52,35 @@ export const arrayOperators: types.OperatorDefinition<any>[] = [
     },
   ] as types.OperatorDefinition<types.ExprConcat>,
 
+  [
+    'push',
+    [],
+    -1,
+    (expr: types.ExprPush, ctx) => {
+      const operand1 = ctx.eval(expr[1], ctx);
+      const arr = clone(util.asArr(operand1));
+      for (let i = 2; i < expr.length; i++) arr.push(ctx.eval(expr[i], ctx));
+      return arr;
+    },
+    (ctx: types.OperatorCodegenCtx<types.ExprPush>): ExpressionResult => {
+      const arrOperand = ctx.operands[0];
+      let arr: Literal | Expression;
+      if (arrOperand instanceof Literal) {
+        arr = new Literal(clone(util.asArr(arrOperand.val)));
+      } else {
+        ctx.link(util.asArr, 'asArr');
+        arr = new Expression(`asArr(${arrOperand})`);
+      }
+      const rArr = ctx.var('' + arr);
+      const pushes: string[] = [];
+      for (let i = 1; i < ctx.operands.length; i++) {
+        const operand = ctx.operands[i];
+        pushes.push(`(${rArr}.push(${operand}))`);
+      }
+      return new Expression(`(${pushes.join(',')},${rArr})`);
+    },
+  ] as types.OperatorDefinition<types.ExprPush>,
+
   [
     'head',
     [],

src/json-expression/types.ts

@@ -200,6 +200,7 @@ export type ExprF64 = BinaryExpression<'f64'>;
 // Array expressions
 export type ArrayExpression =
   | ExprConcat
+  | ExprPush
   | ExprHead
   | ExprSort
   | ExprReverse
@@ -213,6 +214,7 @@ export type ArrayExpression =
   | ExprReduce;
 
 export type ExprConcat = VariadicExpression<'concat' | '++'>;
+export type ExprPush = VariadicExpression<'push'>;
 export type ExprHead = BinaryExpression<'head'>;
 export type ExprSort = UnaryExpression<'sort'>;
 export type ExprReverse = UnaryExpression<'reverse'>;
@@ -320,6 +322,7 @@ export interface OperatorCodegenCtx<E extends Expression> extends JsonExpression
   link: (value: unknown, name?: string) => string;
   const: (js: JavaScript<unknown>) => string;
   subExpression: (expr: Expression) => (ctx: JsonExpressionExecutionContext) => unknown;
+  var: (name: string) => string;
 }
 
 export type OperatorMap = Map<string | number, OperatorDefinition<Expression>>;