Start by clarifying the grammar and semantics, then outline a two-phase approach: a recursive descent parser that builds an AST and an evaluator that walks the AST with an environment stack for lexical scoping. Emphasize robust error handling with specific error types and discuss trade-offs like using exceptions vs. error returns and handling integer overflow with checked arithmetic.
Pro tip: Proactively discuss how you would test the parser and evaluator, including property-based testing for round-trip parsing and fuzzing for error cases. Also, mention that you would separate parsing from evaluation to allow for optimizations like constant folding or lazy evaluation.
Ask questions to pin down the exact syntax, operator precedence, associativity, and scoping rules. Define the grammar formally, including how variables are declared and referenced.
Choose a parsing strategy (e.g., recursive descent) and outline the AST structure. Explain how to handle errors like mismatched parentheses and wrong arity during parsing.
Describe the evaluation process with an environment stack for lexical scoping. Detail how to detect undefined variables and integer overflow, and how to propagate errors.
Enumerate specific error conditions and how they are reported. Discuss strategies for error recovery or fail-fast behavior, and how to provide meaningful error messages.
Compare implementation choices (e.g., recursive descent vs. parser combinators, exceptions vs. result types). Mention potential optimizations and how the design supports them.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clearly defining the evaluator's grammar and input, then describe the recursive descent approach with its call stack, followed by the iterative stack-based approach using an explicit stack. Compare their time and space complexities, highlighting that both are O(n) time but recursive descent uses O(d) stack space where d is nesting depth, while iterative uses O(n) explicit stack space in the worst case.
Pro tip: Mention that recursive descent is more readable and easier to extend for complex grammars, but iterative avoids stack overflow risks on deeply nested inputs—a critical consideration for production systems at scale like Uber's.
Briefly state the evaluator's input (e.g., expression string) and grammar, and clarify that n is the input length. Assume a simple expression grammar for illustration.
Describe how recursive descent uses mutually recursive functions for each grammar rule, with the call stack implicitly managing state. Mention that it's top-down and naturally handles nested structures.
Describe how an explicit stack replaces the call stack, often using a shunting-yard or operator-precedence algorithm. State that it processes tokens linearly and manages state manually.
Both approaches typically run in O(n) time because each token is processed a constant number of times. Note that recursive descent may have overhead from function calls but remains linear.
Recursive descent uses O(d) space for the call stack, where d is the maximum nesting depth (d ≤ n). Iterative uses O(n) space for the explicit stack in the worst case (e.g., deeply nested expressions). Both are O(n) worst-case, but iterative can be more predictable.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Clarify the semantics of the extended set operator, then propose a design that parses multiple bindings into a sequential or simultaneous binding structure. Discuss implementation strategies such as recursive expansion or environment chaining, and analyze trade-offs in evaluation order, scoping, and performance.
Pro tip: Demonstrate awareness of evaluation order and scoping subtleties (e.g., whether bindings are sequential like let* or parallel like let) and mention how this affects the implementation and user expectations.
Ask whether bindings should be evaluated sequentially (like let*) or in parallel (like let), and whether the body can reference all variables. Confirm the expected syntax and behavior.
Propose a parser change to recognize alternating variable-expression pairs, and represent them as a list of bindings. Consider using an intermediate AST node for multiple bindings.
Decide between recursive expansion into nested single-binding set expressions or direct environment manipulation. Discuss pros and cons of each approach.
Ensure correct evaluation order and scoping rules. If sequential, evaluate each expression in the environment extended by previous bindings; if parallel, evaluate all in the original environment.
Discuss performance implications (e.g., repeated environment copying), error handling for odd number of arguments, and potential optimizations like environment chaining.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the requirements: integer division truncating toward zero, and handling division by zero. Then outline the algorithm: check for zero divisor, handle signs separately, compute absolute quotient, and apply sign. Finally, discuss edge cases like overflow and performance.
Pro tip: Mention that many languages (e.g., C, Java) already truncate toward zero, but if implementing from scratch, use absolute values and adjust sign. Also, consider using exceptions or error codes for division by zero based on context.
Confirm that division should truncate toward zero (e.g., -7/2 = -3) and that division by zero should be handled explicitly, perhaps by throwing an exception or returning an error.
Outline steps: check divisor for zero, determine sign of result, compute quotient using absolute values, then apply sign. Consider using bitwise operations for efficiency if needed.
Address overflow (e.g., INT_MIN / -1), negative numbers, and zero dividend. Discuss how to handle division by zero in different contexts (e.g., throw ArithmeticException).
Write pseudocode or actual code, then walk through test cases: positive/negative combinations, zero dividend, division by zero, and overflow scenarios.
Compare approaches: using built-in operators vs. manual implementation, performance implications, and error handling strategies (exceptions vs. error codes).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.