Add special {{@now}} parameter that returns current date in ISO format (#40)

- Modified resolveExpression in compile.ts to handle '@now' identifier
- Added test case for {{@now}} functionality
- {{@now}} is replaced at runtime with new Date().toISOString()

Author: geclos

package.json

@@ -1,6 +1,6 @@
 {
   "name": "promptl-ai",
-  "version": "0.7.5",
+  "version": "0.7.6",
   "author": "Latitude Data",
   "license": "MIT",
   "description": "Compiler for PromptL, the prompt language",
@@ -24,6 +24,7 @@
     "dist"
   ],
   "scripts": {
+    "prepare": "npm run build",
     "dev": "rollup -c -w",
     "build": "rollup -c",
     "build:lib": "rollup -c rollup.config.mjs",

src/compiler/compile.test.ts

@@ -181,6 +181,35 @@ describe('variable assignment', async () => {
     expect(result).toBe('')
   })
 
+  it('special $now parameter returns current date in ISO format', async () => {
+    const prompt = `
+      {{ $now }}
+    `
+    const result = await getCompiledText(prompt)
+    // Check that it's a valid ISO date string (JSON stringified)
+    expect(result).toMatch(/^"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z"$/)
+  })
+
+  it('special $now can be used in expressions', async () => {
+    const prompt = `
+      {{ time = $now }}
+      {{ time }}
+    `
+    const result = await getCompiledText(prompt)
+    // Check that it's a valid ISO date string (JSON stringified)
+    expect(result).toMatch(/^"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z"$/)
+  })
+
+  it('special $now can be used in method calls', async () => {
+    const prompt = `
+      {{ $now.getTime() }}
+    `
+    const result = await getCompiledText(prompt)
+    const timestamp = parseInt(result.trim())
+    expect(timestamp).toBeGreaterThan(0)
+    expect(timestamp).toBeLessThan(Date.now() + 1000) // within 1 second
+  })
+
   it('parameters are available as variables in the prompt', async () => {
     const prompt = `
       {{ foo }}

src/compiler/compile.ts

@@ -34,6 +34,7 @@ import type {
   ResolveBaseNodeProps,
 } from './types'
 import { getCommonIndent, removeCommonIndent } from './utils'
+import { SPECIAL_RESOLVERS } from '../constants'
 
 export type CompilationStatus = {
   completed: boolean
@@ -60,6 +61,7 @@ export class Compile {
   private globalScope: Scope
   private defaultRole: MessageRole
   private includeSourceMap: boolean
+  private builtins: Record<string, () => any>
 
   private messages: Message[] = []
   private globalConfig: Config | undefined
@@ -97,6 +99,7 @@ export class Compile {
     this.ast = ast
     this.stepResponse = stepResponse
     this.defaultRole = defaultRole
+    this.builtins = SPECIAL_RESOLVERS
     this.referenceFn = referenceFn
     this.fullPath = fullPath
     this.includeSourceMap = includeSourceMap
@@ -294,6 +297,7 @@ export class Compile {
     return await resolveLogicNode({
       node: expression,
       scope,
+      builtins: this.builtins,
       raiseError: this.expressionError.bind(this),
     })
   }

src/compiler/logic/index.ts

@@ -27,7 +27,7 @@ export async function updateScopeContextForNode(
   props: UpdateScopeContextProps<Node>,
 ) {
   const type = props.node.type as NodeType
-  if (!nodeResolvers[type]) {
+  if (!updateScopeContextResolvers[type]) {
     throw new Error(`Unknown node type: ${type}`)
   }
 

src/compiler/logic/nodes/assignmentExpression.ts

@@ -136,18 +136,27 @@ async function assignToProperty({
 export function updateScopeContext({
   node,
   scopeContext,
+  builtins,
   raiseError,
 }: UpdateScopeContextProps<AssignmentExpression>) {
   const assignmentOperator = node.operator
   if (!(assignmentOperator in ASSIGNMENT_OPERATOR_METHODS)) {
     raiseError(errors.unsupportedOperator(assignmentOperator), node)
   }
 
-  updateScopeContextForNode({ node: node.right, scopeContext, raiseError })
+  updateScopeContextForNode({
+    node: node.right,
+    scopeContext,
+    builtins,
+    raiseError,
+  })
 
   if (node.left.type === 'Identifier') {
     // Variable assignment
     const assignedVariableName = (node.left as Identifier).name
+    if (assignedVariableName in builtins) {
+      raiseError(errors.assignmentToBuiltin(assignedVariableName), node)
+    }
     if (assignmentOperator != '=') {
       // Update an existing variable
       if (!scopeContext.definedVariables.has(assignedVariableName)) {
@@ -159,7 +168,12 @@ export function updateScopeContext({
   }
 
   if (node.left.type === 'MemberExpression') {
-    updateScopeContextForNode({ node: node.left, scopeContext, raiseError })
+    updateScopeContextForNode({
+      node: node.left,
+      scopeContext,
+      builtins,
+      raiseError,
+    })
     return
   }
 

src/compiler/logic/nodes/identifier.ts

@@ -9,7 +9,14 @@ import type { Identifier } from 'estree'
  * ### Identifier
  * Represents a variable from the scope.
  */
-export async function resolve({ node, scope }: ResolveNodeProps<Identifier>) {
+export async function resolve({
+  node,
+  scope,
+  builtins,
+}: ResolveNodeProps<Identifier>) {
+  if (node.name in builtins) {
+    return builtins[node.name]!()
+  }
   if (!scope.exists(node.name)) {
     return undefined
   }
@@ -19,8 +26,12 @@ export async function resolve({ node, scope }: ResolveNodeProps<Identifier>) {
 export function updateScopeContext({
   node,
   scopeContext,
+  builtins,
   raiseError,
 }: UpdateScopeContextProps<Identifier>) {
+  if (node.name in builtins) {
+    return
+  }
   if (!scopeContext.definedVariables.has(node.name)) {
     if (scopeContext.onlyPredefinedVariables === undefined) {
       scopeContext.usedUndefinedVariables.add(node.name)

src/compiler/logic/types.ts

@@ -26,11 +26,13 @@ type RaiseErrorFn<T = void | never> = (
 export type ResolveNodeProps<N extends Node> = {
   node: N
   scope: Scope
+  builtins: Record<string, () => any>
   raiseError: RaiseErrorFn<never>
 }
 
 export type UpdateScopeContextProps<N extends Node> = {
   node: N
   scopeContext: ScopeContext
+  builtins: Record<string, () => any>
   raiseError: RaiseErrorFn<void>
 }

src/compiler/scan.test.ts

@@ -588,6 +588,33 @@ describe('parameters', async () => {
 
     expect(metadata.parameters).toEqual(new Set(['foo', 'bar', 'arr']))
   })
+
+  it('does not include special identifiers as parameters', async () => {
+    const prompt = `
+      {{ $now }}
+    `
+
+    const metadata = await scan({
+      prompt: removeCommonIndent(prompt),
+    })
+
+    expect(metadata.parameters).toEqual(new Set())
+  })
+
+  it('raises error when assigning to builtin', async () => {
+    const prompt = `
+      {{ $now = "2023-01-01" }}
+    `
+
+    const metadata = await scan({
+      prompt: removeCommonIndent(prompt),
+    })
+
+    expect(metadata.errors).toHaveLength(1)
+    expect(metadata.errors[0]!.message).toBe(
+      "Cannot assign to builtin variable: '$now'",
+    )
+  })
 })
 
 describe('referenced prompts', async () => {

src/compiler/scan.ts

@@ -4,6 +4,7 @@ import {
   CUSTOM_MESSAGE_ROLE_ATTR,
   REFERENCE_DEPTH_LIMIT,
   REFERENCE_PATH_ATTR,
+  SPECIAL_RESOLVERS,
   TAG_NAMES,
 } from '$promptl/constants'
 import CompileError, { error } from '$promptl/error/error'
@@ -57,6 +58,7 @@ export class Scan {
   private withParameters?: string[]
   private requireConfig: boolean
   private configSchema?: z.ZodType
+  private builtins: Record<string, () => any>
 
   private config?: Config
   private configPosition?: { start: number; end: number }
@@ -95,6 +97,7 @@ export class Scan {
     this.withParameters = withParameters
     this.configSchema = configSchema
     this.requireConfig = requireConfig ?? false
+    this.builtins = SPECIAL_RESOLVERS
 
     this.resolvedPrompt = document.content
     this.includedPromptPaths = new Set([this.fullPath])
@@ -194,6 +197,7 @@ export class Scan {
     await updateScopeContextForNode({
       node,
       scopeContext,
+      builtins: this.builtins,
       raiseError: this.expressionError.bind(this),
     })
   }

src/constants.ts

@@ -40,3 +40,8 @@ export enum KEYWORDS {
 
 export const RESERVED_KEYWORDS = Object.values(KEYWORDS)
 export const RESERVED_TAGS = Object.values(TAG_NAMES)
+export const SPECIAL_IDENTIFIERS = new Set(['$now'])
+
+export const SPECIAL_RESOLVERS: Record<string, () => unknown> = {
+  $now: () => new Date(),
+}