93 research outputs found
Forty hours of declarative programming: Teaching Prolog at the Junior College Utrecht
This paper documents our experience using declarative languages to give
secondary school students a first taste of Computer Science. The course aims to
teach students a bit about programming in Prolog, but also exposes them to
important Computer Science concepts, such as unification or searching
strategies. Using Haskell's Snap Framework in combination with our own
NanoProlog library, we have developed a web application to teach this course.Comment: In Proceedings TFPIE 2012, arXiv:1301.465
Linear, bounded, functional pretty-printing
We present two implementations of Oppen's pretty-printing algorithm in Haskell that meet the efficiency of Oppen's imperative solution but have a simpler, clear structure. We start with an implementation that uses lazy evaluation to simulate two co-operating processes. Then we present an implementation that uses higher-order functions for delimited continuations to simulate co-routines with explicit scheduling
Constructing functional programs for grammar analysis problems
Abstract This paper discusses the derivation of functional programs for grammar analysis problems, such as the EMPTY problem and the REACH-ABLE problem. Grammar analysis problems can be divided into two classes: top-down problems such as FOLLOW and REACH-ABLE, which are described in terms of the contexts of nonterminals, and bottom-up problems such as EMPTY and FIRST, which do not refer to contexts. In a previous paper we derive a program for bottom-up grammar analysis problems. In this paper we derive a program for top-down grammar analysis problems by transforming the specification of an arbitrary top-down problem into a program. The existence of a solution is guaranteed provided some natural conditions are satisfied. Furthermore, we describe a general transformation that applies to both classes of grammar analysis problems. The result of this transformation is a program that avoids unnecessary computations in the computation of a fixed point. Constructor classes, which are used to abstract from the notions bottom-up and top-down, are an essential ingredient of the latter derivation
Hindley-Milner Elaboration in Applicative Style
International audienceType inference—the problem of determining whether a program is well-typed—is well-understood. In contrast, elaboration—the task of constructing an explicitly-typed representation of the program— seems to have received relatively little attention, even though, in a non-local type inference system, it is non-trivial. We show that the constraint-based presentation of Hindley-Milner type inference can be extended to deal with elaboration, while preserving its elegance. This involves introducing a new notion of "constraint with a value", which forms an applicative functor
A Typed, Algebraic Approach to Parsing
In this paper, we recall the definition of the context-free expressions (or µ-regular expressions), an algebraic presentation of the context-free languages. Then, we define a core type system for the context-free expressions which gives a compositional criterion for identifying those context-free expressions which can be parsed unambiguously by predictive algorithms in the style of recursive descent or LL(1).
Next, we show how these typed grammar expressions can be used to derive a parser combinator library which both guarantees linear-time parsing with no backtracking and single-token lookahead, and which respects the natural denotational semantics of context-free expressions. Finally, we show how to exploit the type information to write a staged version of this library, which produces dramatic increases in performance, even outperforming code generated by the standard parser generator tool ocamlyacc
LL(1) Parsing with Derivatives and Zippers
In this paper, we present an efficient, functional, and formally verified
parsing algorithm for LL(1) context-free expressions based on the concept of
derivatives of formal languages. Parsing with derivatives is an elegant parsing
technique, which, in the general case, suffers from cubic worst-case time
complexity and slow performance in practice. We specialise the parsing with
derivatives algorithm to LL(1) context-free expressions, where alternatives can
be chosen given a single token of lookahead. We formalise the notion of LL(1)
expressions and show how to efficiently check the LL(1) property. Next, we
present a novel linear-time parsing with derivatives algorithm for LL(1)
expressions operating on a zipper-inspired data structure. We prove the
algorithm correct in Coq and present an implementation as a parser combinators
framework in Scala, with enumeration and pretty printing capabilities.Comment: Appeared at PLDI'20 under the title "Zippy LL(1) Parsing with
Derivatives
A principled approach to REPL interpreters
Read-eval-print-loops (REPLs) allow programmers to test out snippets of code, explore APIs, or even incrementally construct code, and get immediate feedback on their actions. However, even though many languages provide a REPL, the relation between the language as is and what is accepted at the REPL prompt is not always well-defined. Furthermore, implementing a REPL for new languages, such as DSLs, may incur significant language engineering cost. In this paper we survey the domain of REPLs and investigate the (formal) principles underlying REPLs. We identify and define the class of sequential languages, which admit a sound REPL implementation based on a definitional interpreter, and present design guidelines for extending existing language implementations to support REPL-style interfaces (including computational notebooks). The obtained REPLs can then be generically turned into an exploring interpreter, to allow exploration of the user’s interaction.The approach is illustrated using three case studies, based on MiniJava, QL (a DSL for questionnaires), and eFLINT (a DSL for normative rules). We expect sequential languages, and the consequent design principles, to be stepping stones towards a better understanding of the essence of REPLs.</p
- …