Hiring guide for APL Engineers

APL Developer Hiring Guide

APL (A Programming Language) is a high-level, interactive programming language known for its distinctive array processing capabilities. The language was developed in the 1960s by Kenneth E. Iverson while at IBM, as detailed in his book "A Programming Language" (source: Iverson K.E., Wiley, 1962). APL is unique due to its use of non-alphanumeric symbols for both arithmetic and data manipulation operations. Its influence can be seen in later array languages such as J and K (source: "The J Programming Language", Roger Hui). Despite its age, APL continues to be used today, especially in areas involving complex data analysis or mathematical modeling (source: "The Past, Present and Future of APL", SIGAPL conference).

Ask the right questions secure the right APL talent among an increasingly shrinking pool of talent.

First 20 minutes

General APL app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in APL application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you define APL's array programming model?
APL's array programming model is a paradigm where data is represented as arrays and operations are performed on these arrays as a whole rather than on individual elements. This allows for concise and expressive code.
What are the basic data types in APL?
The basic data types in APL are numeric (including both integers and floating-point numbers), character (representing individual characters), and arrays (which can hold any combination of numeric and character data).
Describe the difference between scalar and non-scalar functions in APL.
Scalar functions in APL operate element-wise on arrays, meaning they perform their operation on each element of the array individually. Non-scalar functions, on the other hand, can manipulate the array as a whole.
How would you use the iota function in APL?
The iota function in APL is used to generate a vector of consecutive integers. For example, '?5' would generate the vector 1 2 3 4 5.
What are the uses of the rho function in APL?
The rho function in APL has two main uses. It can be used to reshape an array, changing its dimensions while keeping its elements, or it can be used to find the shape of an array, returning a vector that represents the array's dimensions.
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What you’re looking for early on

Does the candidate demonstrate a clear understanding of APL programming language?
Can the candidate effectively communicate their thought process?
Does the candidate show good problem-solving skills?
Is the candidate familiar with the tools and technologies that are used in your organization?

Next 20 minutes

Specific APL development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

Describe the difference between monadic and dyadic functions in APL.
Monadic functions in APL are functions that take one argument, while dyadic functions take two arguments. The behavior of a function can change depending on whether it is used monadically or dyadically.
How would you implement a matrix multiplication in APL?
Matrix multiplication in APL can be implemented using the inner product operator '.+'. For example, if A and B are matrices, then the expression 'A .+.× B' would compute the matrix product of A and B.
What are the uses of the commute function in APL?
The commute function in APL, represented by the symbol '~', has two main uses. It can be used to reverse the order of arguments to a dyadic function, or it can be used monadically to create a function that returns the set difference of its arguments.
Describe the difference between explicit and tacit programming in APL.
Explicit programming in APL involves writing out each step of a computation in detail, while tacit programming involves defining computations in terms of the transformations they perform on data, without specifying the data itself. Tacit programming can lead to more concise and expressive code.
How would you implement a quicksort algorithm in APL?
A quicksort algorithm in APL can be implemented in a very concise way using the grade up function '?'. For example, if V is a vector, then 'V[?V]' would return a sorted version of V.
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The ideal back-end app developer

What you’re looking to see on the APL engineer at this point.

At this point, a skilled APL engineer should demonstrate strong problem-solving abilities, proficiency in APL programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with APL.

What does the following APL code do? `5 3 2 + 4 2 1`
5 3 2 + 4 2 1
This code performs element-wise addition of two vectors. The output will be a vector of `9 5 3`.
What will be the output of the following APL code? `?10`
This code generates a vector of the first 10 natural numbers starting from 1. The output will be `1 2 3 4 5 6 7 8 9 10`.
What does the following APL code do? `3 3??9`
3 3??9
This code generates a 3x3 matrix with the first 9 natural numbers. The output will be a matrix with rows `1 2 3`, `4 5 6`, and `7 8 9`.
What will be the output of the following APL code? `2 2??4`
2 2??4
This code generates a 2x2 matrix with the first 4 natural numbers. The output will be a matrix with rows `1 2` and `3 4`.

Wrap-up questions

Final candidate for APL Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle APL application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What are the uses of the enclose and disclose functions in APL?
The enclose function in APL, represented by the symbol '?', is used to group elements of an array into a single element, while the disclose function, represented by the symbol '?', is used to separate a grouped element back into its constituent elements.
Describe the difference between the execute and format functions in APL.
The execute function in APL, represented by the symbol '?', is used to evaluate a string of APL code, while the format function, represented by the symbol '?', is used to convert APL data into a string representation.
How would you handle errors in APL?
Errors in APL can be handled using the error guard function '?EA'. This function takes a string of APL code as its right argument and a value as its left argument. If the code produces an error, the function returns the left argument; otherwise, it returns the result of the code.

APL application related

Product Perfect's APL development capabilities

Beyond hiring for your APL engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in APL projects, and can engage in multiple capacities.