(ast: AST): ast is UndefinedWhen to use
Use to identify AST nodes that represent exactly the JavaScript undefined
value.
Source effect/SchemaAST.ts:1421 lines
export const const isUndefined: (
ast: AST
) => ast is Undefined
function makeGuard<T extends AST["_tag"]>(
tag: T
): (ast: AST) => ast is Extract<AST, { _tag: T }>