title: SML vs. Haskell

Comparison of ML and Haskell

Similarities

There are lots!

  • Functions are values, arbitrary higher-order functions
  • Algebraic data types + pattern matching
  • Hindley-Milner type inference
  • Parametric polymorphism

Some differences

Haskell features

  • Purity!
    • Referential transparency: always safe to substitute x = y
    • Side effects are reflected in the type system
    • More parallelizable
  • Lazy evaluation
    • Separation of concerns
    • Trivially support infinite data structures
  • Cleaner syntax, nice sugar
    • Far fewer keywords, better consistency
    • Nice sugar for monadic programming and list comprehensions
  • Type classes
    • Less powerful than SML’s modules, more convenient; sweet spot?
    • Nicer solution to equality and operator overloading
  • Minimalistic module system
    • Manages namespace only

SML features

  • Arbitrary side-effects
    • Often convenient
    • Pure functions are considered good style
  • Strict evaluation
    • Easier to reason about time and (especially) space performance
    • Some theoretical advantages (one bottom per type)
  • Expressive module system
    • Separates module interfaces (signatures) from implementation (structures)
    • Allows many-to-many relationships between them
    • Supports hierarchical modules and parameterized modules (functors)
    • Not tied to the file system


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