import { SourceBasedExpression } from '../Expression' ; import { OclExecutionContext } from '../../OclExecutionContext' ; oclExpression oclExample export class FirstExpression extends SourceBasedExpression { evaluate ( visitor , localVariables ? ) { const source = this . getSource ( ) . evaluate ( visitor , localVariables ) ; if ( source instanceof Array ) { return source [ 0 ] ; } } }