Patterns as objects in grace

Abstract

Object orientation and pattern matching are often seen as conflicting approaches to program design. Object oriented programs place type-dependent behaviour inside objects and invoke it via dynamic dispatch, while pattern matching programs place type-dependent behaviour outside data structures and invoke it via multiway conditionals (case statements). Grace is a new, dynamic, object-oriented language designed to support teaching: to this end, Grace needs to support both styles. In this paper we explain how this conflict can be resolved gracefully: by modelling patterns and cases as partial functions, reifying those functions as first-class objects, and then building up complex patterns from simpler ones using pattern combinators. We describe our design for pattern matching in Grace, and its implementation as an object-oriented framework.

Open pattern matching for C++

“…This "patterns as objects" approach has been explored in several different languages [11,14,34,47]. Implementations differ in where bindings are stored and what is returned as a result, but in its most basic form it consists of the pattern interface with a virtual function match that accepts a subject and returns whether it was accepted or rejected.…”

“…The solution is remarkable in that unlike most of the library approaches to open pattern matching, it does not rely on naïve backtracking and, in fact, encodes the optimized algorithm based on backtracking automata [1,21]. Grace is another programming language that provides a library solution to pattern matching through objects [14]. Similar to other control structures in the language, Grace encodes the match statement with partial functions and lambda expressions, while patterns are encoded as objects.…”

Modules as gradually-typed objects

“…Along with methods, types may be included as components of objects. Types have a runtime representation as a pattern [10] object.…”

The semantics of name resolution in grace

“…Other language features (e.g. classes, traits and modules) are defined in terms of these concepts [4,17,18]. There are two mainstream implementations: a Grace to C compiler and a Grace to JavaScript transpiler.…”