Helium: HaskellLight Compiler Framework for Teaching

Introducing HaskellLight Rijk-Jan, Arjan, Daan, Martijn L.

Goal • Teaching • “Compiler framework” Haskell

Demo

Language Haskell Error reporting No classes Compiler Simplicity Error reporting eXtreme testing Design

Highlights • Precise positions of errors • Warnings • Hints (type errors, undefined var.) • Still fast, small and portable

Position f = 3 x = 3 f = 4 • Hugs: • ERROR Main.hs:1 - "f" multiply defined • Where is the other definition? • Helium: • (1, 1), (3, 1): duplicated function "f"

Warnings f id = id 3 id x = x • Which “id” was meant? • Hugs • Silent • Helium • (1, 3): variable "id" shadows the one at (3, 1)

Warnings • Unused parameters/functions... • No type definition • Unreachable code (in case)

Hints map f xs = case xs of []->[] y:ys->map ys • ERROR Main.hs:1 – Type error in function binding*** Term : map*** Type : c -> [a] -> [b]*** Does not match : [a] -> [b] • (4, 11): type error in rhs of case: map ystype: b -> cprevious rhs’s: [a]Probably too few arguments to 'map' in this right-hand side

Fast, small, portable

Code speed GHC  5 x Helium  60 x Hugs

Implementation Lexer Lazy Virtual Machine (Daan Leijen) Parser ToCore Static Analysis Type Checker

Not yet modules where, lambda Float, tuples pattern-matching nested patterns comprehensions FFI (Java), GUI, IDE, interpreter “Never” classes Double, Integer records Future of Helium

Conclusion • Helium is Haskell-- with nice error messages • Helium will be “textbook Haskell” • Helium will hopefully some day be used in education

Helium: HaskellLight Compiler Framework for Teaching