A persistent collections library for Python.
pcollections is a library of persistent (immutable) collections inspired by
the immutable data structures of Clojure but built to resemble
the native Python collections as closely as possible. The library is implemented
in Python but employs the phamt
(Persistent Hash Array Mapped Tries) library, which is implemented in C, to
perform efficient low-level operations.
The library implements three persistent types: plist, pset, and
pdict. These are immutable versions of the builtin list, set, and dict
types. The persistent object interfaces are as similar as possible to the native
types, but the method signatures differ in ways necessary to accomodate
efficient immutable ways of doing things. For example, the pdict constructor
is identical to the dict constructor and always returns a pdict equal to the
dict that would be created with the same arguments. However, instead of
supporting operations like d[key] = val, pdicts support a set method: d = d.set(key, val).
In addition to the persistent types, there are two lazy types, llist and
ldict. These types are enabled by the lazy type. A lazy object is
basically a partial object that, when called, caches the function's return
value and returns that value without rerunning the function on subsequent
calls. The llist and ldict types are equivalent to the plist and pdict
types with one exception. Elements of an llist and values of an ldict that
are of the lazy type are dereferenced when requested. This allows a programmer
to easily create data structures (potentially nested data structures) whose
items are the results of complex or long-running computations that only get
computed once requested. The persistent data structures allow the arguments to
these lazy functions to be safe from mutation.
Finally, the persistent and lazy types have transient correlaries that enable
more efficient batch-mutation of the persistent types. The transient types
tlist, tset, tdict, tllist, and tldict all have interfaces equivalent
to their standard mutable correlaries (transient types are mutable).
MIT License
Copyright (c) 2022-2023 Noah C. Benson
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