Stub out @if keyword expression

Author: mkantor

src/language/compiling/semantics/keyword-handlers/if-handler.ts

@@ -0,0 +1,14 @@
+import either, { type Either } from '@matt.kantor/either'
+import type { ElaborationError } from '../../../errors.js'
+import {
+  type Expression,
+  type ExpressionContext,
+  type KeywordHandler,
+  type SemanticGraph,
+} from '../../../semantics.js'
+
+export const ifKeywordHandler: KeywordHandler = (
+  _expression: Expression,
+  _context: ExpressionContext,
+): Either<ElaborationError, SemanticGraph> =>
+  either.makeLeft({ kind: 'bug', message: 'not implemented' })

src/language/compiling/semantics/keywords.ts

@@ -2,6 +2,7 @@ import { type KeywordHandlers } from '../../semantics.js'
 import { applyKeywordHandler } from './keyword-handlers/apply-handler.js'
 import { checkKeywordHandler } from './keyword-handlers/check-handler.js'
 import { functionKeywordHandler } from './keyword-handlers/function-handler.js'
+import { ifKeywordHandler } from './keyword-handlers/if-handler.js'
 import { indexKeywordHandler } from './keyword-handlers/index-handler.js'
 import { lookupKeywordHandler } from './keyword-handlers/lookup-handler.js'
 import { panicKeywordHandler } from './keyword-handlers/panic-handler.js'
@@ -24,6 +25,11 @@ export const keywordHandlers: KeywordHandlers = {
    */
   '@function': functionKeywordHandler,
 
+  /**
+   * Conditionally evaluates one of two expressions based on a boolean value.
+   */
+  '@if': ifKeywordHandler,
+
   /**
    * Returns the value of a property within an object.
    */

src/language/semantics/keyword.ts

@@ -2,6 +2,7 @@ export const isKeyword = (input: string) =>
   input === '@apply' ||
   input === '@check' ||
   input === '@function' ||
+  input === '@if' ||
   input === '@index' ||
   input === '@lookup' ||
   input === '@panic' ||