Composable_Building_Blocks.md

Composable Building Blocks

The Holy Grail of programming language design is to create a simple yet powerful language with a small number of orthogonal building blocks that can be composed together in many ways.

Design Strategies for Composability:

• declarative semantics
• orthogonality
  • unify features that are almost the same, but with unnecessary differences
  • split up features that do two things at once into separate features that can be composed
• eliminate the need to write "glue" code when composing elements, by using standard interfaces
• remove restrictions on how language elements can be composed
• eliminate syntactic overhead for common compositions

Composability Failure in OpenSCAD:

• Can't pass a function as an argument to a module for generalized extrusion. Fix: First Class Values.
• Can't compose for with intersection. Fix: this is the module composability problem.
• concat has a variable-length argument list, and can't be composed with an expression that generates a sequence of lists to be concatenated, eg a for loop, so users implement flatten instead. In Haskell, concat takes a single argument, which is a list of lists: this makes Haskell's concat highly composable, and eliminates the need for a separate flatten function.
• Can't compose children() with for, eg for (shape=children()) .... Fix: Generic Sequences.
• Ranges can be composed with for, but can't be interchanged with lists of number in other contexts. Fix: Generic Sequences.

Bibliography

• http://stackoverflow.com/questions/2887013/what-does-composability-mean-in-context-of-functional-programming