Sketchbook: Penknife standard library

The Penknife standard library will build upon the basic features of Penknife with a few extra DSLs and frameworks for basic data manipulation.

None of the features described here actually exist yet.

Patterns and lenses

Binding patterns: The pattern applies to a single value, and it may bind any number of local variables. This will be used by let.

List tail binding patterns: The pattern has access to a sub-pattern that applies "next." It operates on a single value and may bind any number of local variables. For most patterns, the argument is assumed to be a list, and the pattern consumes some values from the list before passing the tail to the sub-pattern. This feature will be used for the argument lists of utilities like fn.

Every definition of a binding pattern also defines a list tail binding pattern.

Assignment patterns: In a place block, this pattern returns a pair of a getter and an optional setter. The put block uses it for assignment.

Lens patterns: In a lens block, this pattern returns either a getter thunk (like the type (() !-> b)) or a lens implementation (like the type (a -> (b * (b -> a)))), where the types are interpreted as follows:

• (_ * _) is a type representing Penknife's (cons _ _) values.
• (_ -> _) is a type representing Penknife's functions whose input is a one-element list and whose yoke input is pure.
• (() !-> _) is a type representing Penknife's functions whose input is a zero-element list and whose yoke input is impure.

Every definition of a lens pattern also defines a binding pattern, a list tail binding pattern, an assignment pattern, and a lens object. The lens object is callable (like the type (a -> b)).

Every definition of a structure type also defines a lens pattern, a binding pattern, a list tail binding pattern, an assignment pattern, and a type object.

Effects

Some of the standard library's utilities expect their yoke object to implement the following method:

(yoke-get-mbox-env yoke): Gets a default environment for mutable boxes. Furthermore, the standard library usually deals with mutable box objects that carry their own environment token for more convenient manipulation.

Ad-hoc polymorphic tools

Penknife's standard library tools are a big mess of weak typing and surprise behaviors. Don't worry about it!^TM

Weak typing: Most tools that process lists will also treat natural numbers as lists of (nil). Most tools that process natural numbers will also treat lists as numbers based on their length.

Comparison: compare lt lte is

Lists and maps: foldl foldr map mappend keep rem any all each rev keys cut

call: On a list or map, looks up an element by key.

find: Takes a list and a predicate and returns (nil) or (list key elem) where elem satisfies the predicate.

kvs: Takes a list or map and returns a list of two-element lists containing the keys and values.