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Designing Types for R Empirically

Reviewed by Greg Wilson / 2022-03-23
Keywords: Programming Languages, Types

I have a love-hate relationship with R. On the one hand, it's a lot easier to teach data science and plotting to novices with R's tidyverse libraries than it is using Python's Pandas. On the other hand, the underlying language isn't just quirky: it's downright eccentric, and those eccentricities are an endless source of frustration.

I don't think R itself will ever be changed in significant ways, but work like Turcotte2020 can guide incremental improvements and shape an evidence-based design of whatever eventually comes next. As the authors say:

We implemented Typetracer, an automated tool for extracting types from execution traces of R programs. The goal of this tool is to output a tuple ⟨f ,t1, . . . ,tn,t⟩ for each function call during the execution of a program, where f is an identifier for a function, ti are type-level summaries of the arguments and t is a summary of the return value. While seemingly simple, the details and their proverbial devil are surprisingly tricky to get right at scale.

They then selected over 400 packages containing more than 750K lines of R and half a million lines of native code in C and Fortran and checked function signatures for 792 code kernels downloaded from Kaggle. With that data in hand, they examined how well their proposed typing system could capture the types used in real-world settings. The discussion section then explores design alternatives suggested by what their proposed system couldn't do or couldn't do well. As with the recently-reviewed article on Python 3 types, this work shows that programming language design is moving from "theory plus strong opinions" to being an empirically-grounded discipline.

Turcotte2020 Alexi Turcotte, Aviral Goel, Filip Křikava, and Jan Vitek: Designing types for R, empirically. Proc. OOPSLA 2020, doi:10.1145/3428249.

The R programming language is widely used in a variety of domains. It was designed to favor an interactive style of programming with minimal syntactic and conceptual overhead. This design is well suited to data analysis, but a bad fit for tools such as compilers or program analyzers. In particular, R has no type annotations, and all operations are dynamically checked at run-time. The starting point for our work are the two questions: what expressive power is needed to accurately type R code? and which type system is the R community willing to adopt? Both questions are difficult to answer without actually experimenting with a type system. The goal of this paper is to provide data that can feed into that design process. To this end, we perform a large corpus analysis to gain insights in the degree of polymorphism exhibited by idiomatic R code and explore potential benefits that the R community could accrue from a simple type system. As a starting point, we infer type signatures for 25,215 functions from 412 packages among the most widely used open source R libraries. We then conduct an evaluation on 8,694 clients of these packages, as well as on end-user code from the Kaggle data science competition website.