@umpire/dsl

Pure expression DSL and compiler helpers for Umpire.

When to use this vs @umpire/json

Reach for @umpire/dsl when your rules live entirely in TypeScript — no serialization, no JSON schemas, no round-tripping across runtimes. If you need expr.check() or rules that survive a JSON boundary, use @umpire/json instead. Its expr is a superset and covers everything here.

Example

A scheduler form where endDate is only available once the user has set a startDate and chosen a recurrence mode other than 'none':

import { expr, compileExpr } from '@umpire/dsl'
import { umpire, enabledWhen } from '@umpire/core'

const endDateEnabled = compileExpr(
  expr.and(expr.present('startDate'), expr.neq('recurrence', 'none')),
  { fieldNames: new Set(['startDate', 'recurrence']) },
)

const ump = umpire({
  fields: {
    startDate: {},
    recurrence: {},
    endDate: {},
    timezone: {},
  },
  rules: [enabledWhen('endDate', endDateEnabled)],
})

ump.check({
  startDate: '2026-06-01',
  recurrence: 'weekly',
  endDate: null,
  timezone: 'UTC',
})
// endDate: { enabled: true, required: false, satisfied: false }

ump.check({
  startDate: null,
  recurrence: 'none',
  endDate: null,
  timezone: 'UTC',
})
// endDate: { enabled: false, required: false, satisfied: false }

API

| Export | What it is | | ---------------------------------- | ---------------------------------------------------------------------------------------------------------------------------- | | expr | Expression builder — expr.present(), expr.neq(), expr.and(), and the rest | | compileExpr(expression, options) | Turns an Expr into a (values, conditions) => boolean predicate; validates field and condition references at compile time | | getExprFieldRefs(expression) | Returns the unique field names referenced by an expression | | Expr | Union type of all expression AST nodes | | ExprBuilder<F, C> | Typed shape of expr, parameterized over field names and condition keys |

For the full expr.* method table, see the docs page.