Language Qualities

These are properties or qualities of any Haskell standard we would like to preserve or make sure the language has. This is not about certain extensions or libraries the language should have, but rather properties of the language as a whole.

• import-safe - importing a new module can never silently change the behavior of a program, but it may cause a compile-time error. two programs that are identical except one has a superset of the imports of the other will either behave identically or at least one will fail to compile. (e.g. OverlappingInstances breaks this)

• independent of the evaluation order. The report does not specify nor require lazy evaluation as an evaluation strategy, it only specifies a non-strict semantics.

• admits an efficient implementation. features that require large amounts of run-time support or non-trivial restrictions on the implementation method should be avoided. (this is a tradeoff and the design space of haskell implementations has not fully been explored so we should be conservative when we can)

• transformation safe. the language will not have features that cause common optimizations and transformations to become non-meaning-preserving. All lambda calculus transformations should apply. (this is broken by the MonomorphismRestriction (eta-reduction/expansion) and ImplicitParams (beta-reduction))

• sufficiently expressive and convenient for most purposes. We should try to avoid standardizing on something that will be routinely ignored.

• clearly and precisely specified (concise also desirable). It would be good to make the informal notion of the Haskell'98 core language more precise and formal.

• avoids special cases where possible.

• tested by experience, though a little innovation may be necessary to meet the other objectives.

• To modify a phrase a bit "It should make easy things unneccesary and difficult things easy."