FUNCTIONAL PROGRAMING AT WORK - HASKELL AND DOMAIN SPECIFIC LANGUAGES Dr. John Peterson Western State Colorado University

Project Pitch Let’s talk! I’ll set up wiki accounts tonight Good things: A well defined scope that allows an incremental approach Pre-existing infrastructure A compositional point of view (building-block pieces + combining functions) Novel semantic foundation (reactive programming, for example)

Quiz 4 Advantages / disadvantages of Haskell embedding Euterpea expressions that are the same in Euterpea but not Haskell. Why does this matter? What is the semantic model of Euterpea? What does a parser know that a grammar doesn’t?

Homework 5 eek_5

HW5 Project Organization Phase 1: a parsec parser that converts strings to tokens Create a data type for lexemes Drop whitespace Group characters for variables / numbers Represent indentation at the start of a line Don’t worry about error reporting Test before proceeding!

HW5 Phase 2 Deal with layout (indentation): Map a list of tokens that includes indentation to a list that drops indentation and replaces it with a new token, End Probably don’t need to use parsec Need to know all outer indentation levels (list of int will work)

Phase 2 Strategy Line indented more than current level Line indented at current level Line indented less than current level How do we recognize a new level? Assume all blocks have at least one statement Ignore blank lines in lexer

Phase 3 Strategy Use “End” to mark line end and block end Should look like grammar Use “try” for backtracking. Where do we need to worry about backtracking?

Questions?

Haskell Modules Modules – group a set of names in a file. Strictly a renaming construct – deals with visibility only. Use modules to encapsulate functionality – like ast.hs You can do selective export (export lists) or import (import lists) Hierarchical namespace uses “.”

Applicative and Functor se/latest/doc/html/Data-Functor.html#v: se/latest/doc/html/Control-Applicative.html#v: What do these infix operators do for parsers?

Inside parsec See Let’s look at “Char”, “Combinator”, and “Prim” How can we make combinators similar to those in Char with an arbitrary token stream type?