Professor Fish

Admittedly, the illustrative partial evaluator of the previous blog post was quite limited. Consider, for example, the following attempts of partially evaluating different applications of the exponentiation function; the last attempt diverges: > peval (lib, (Apply "exp" [Const 2, Const 3])) Const 8 > peval (lib, (Apply "exp" [Var "x", Const 3])) Binary Times (Var "x") (Binary Times (Var "x") (Binary Times (Var "x")(Const 1))) > peval (lib, (Apply "exp" [Const 2, Var "n"])) IfZero (Var "n") (Const 1) (Binary Times (Const 2) (IfZero (Binary Plus (Var "n") (Const (-1))) (Const 1) (Binary Times (Const 2) (IfZero (Binary Plus (Binary Plus (Var "n") (Const (-1))) (Const (-1))) (Const 1) (Binary Times (Const 2) (IfZero (Binary Plus (Binary Plus (Binary Plus (Var "n") (Const (-1))) (Const (-1))) (Const (-1))) (Const 1) (Binary Times (Const 2) (IfZero (Binary Plus (B...

Let's understand the basic mechanics of a (too?) simple online partial evaluator . (I am grateful to William Cook for encouraging the following Haskell exercise, and for sharing with me some stimulating slides and notes on the subject.) I recommend John Hatcliff's excellent and detailed course material on "Foundations of Partial Evaluation and Program Specialization"---available online . For those in a hurry, try Wikipedia . Anyway, partial evaluation, macro systems, and multi-stage programming is a lot of fun. Here is also a paper (draft) by William Cook that I can warmly recommend. Consider the following syntax of a simple, pure, first-order, functional programming language: type Prog = (FEnv,Expr) type FEnv = [FDef] type FDef = (String,([String],Expr)) data Expr = Const Int | Var String | Binary Op Expr Expr | IfZero Expr Expr Expr | Apply String [Expr] deriving (Show) data Op = Plus | Times deriving (Show) Thus, a program consists of a main expression and...

Dear language researchers and engineers, if you were interested in empirical studies of software languages , what journals and conferences come to your mind as potential publication venues for such studies? In different terms, what do you think what quality journals and conferences would be popping up if you were googling (binging) intelligently for empirical studies of programming languages, modeling languages, domain-specific languages, and other software languages you can think of? Please send your ideas by email to rlaemmel@acm.org by 19 May. The results of this inquiry will be published while preserving anonymity of all participants. Thanks! Professor Fish PS1: The reason for asking is that we are into a meta-empirical effort, continuing our SLE 2010 paper " Empirical language analysis in software linguistics " (Jean-Marie Favre and Dragan Gasevic and Ralf Lämmel and Ekaterina Pek). We are going to use content analysis , where we aim for automation for data mining to t...

I enjoyed reading recently " Language Implementation Patterns: Create Your Own Domain-Specific and General Programming Languages " by Terence Parr (the ANTLR guy) as available from The Pragmatic Bookshelf . The book uses a design pattern style to present techniques for language processing. Eventually the book gets to leverage ANTLR for many problems, but it also explains language processing in terms of patterns that require regular programming effort without the help of a program generator. This is a clever way of teaching some basics of grammars, parsing, tree walking and other concepts that can be explained all too easily (elsewhere) in a too complicated manner, or in a manner requiring substantial background. In my (very) advanced Bachelor's course Programming techniques and technologies , I face students who don't know much yet about formal languages and certainly nothing about compiler construction; they are aware though of context-free grammars (EBNFs) for the p...

(C) 2011, Ralf Laemmel Let's map Knuth' attribute grammar example to Haskell. This has been done many times. In fact, there is a long track of excellent research on the relation between attribute grammars and functional programming. For instance, see the work by Doaitse Swierstra and team over many years. Our development here is meant to just illustrate the basic mapping in an as simple and self-contained manner as possible. One should notice that the chosen example (due to Knuth) requires laziness for the straightforward encoding that is leveraged below. Hence, C programmers are encouraged to try to transcribe this Haskell program to their favorite language. The following context-free grammar is assumed: digit : '0' digit : '1' digits : digit digits : digits digit number : digits number : digits '.' digits That is, we deal with binary numbers---both integer and fractional numbers. We use the following algebraic datatypes to model the grammar: data Digit...