Tools and Utilities for 'compiling' trees of Dynamic functions into statically typed values

This package consists of two modules: Data.Dynamic.Resolve.Utils that contains various utility functions for working with Data.Dynamic's Dynamics (particularly for dealing with Monads, Functors, and Applicatives), and Data.Dynamic.Resolve, which contains higher-level functions for applying chains of Dynamic-wrapped functions safely, with good error information, and with support for multiple possible values for a given parameter. This readme will focus on the latter.

Quick Notes

Many functions in this library have a type variable env that is not used within the rest of the type signature (because it is swallowed by the Dynamics) and so cannot be inferred by GHC. The easiest way to specify it is with the TypeApplications extension. env is a monad representing the 'environment' that your functions should be resolved in, and is used to allow pure and monadic values of the specified type to be fed into one another without explicit binds. This is useful for, for example, evaluating a language that can do IO, and doesn't share Haskell's level of separation of effects. If this is undesirable, pure versions are also provided (which usually simply use Identity for env).

Usage Overview

1. Make whatever type you're using to carry around your Dynamics an instance of Parameter, which requires a values function which returns a NonEmpty list of Dynamics, representing the possible values of that parameter.

2. For simple usage, invoke reifyList <function parameter> <list of argument parameters>. It will return Either information about where the chain of function application failed, or the desired type.

3. For more advanced usage, build a Tree of function application and use reifyTree. Application trees are evaluated by first evaluating fully the left and right subtrees of a given branch, and then applying the result of the left subtree to the result of the right subtree. Here are some examples of function applications and their corresponding application trees (note that in actual code, the values would be wrapped inside Parameters):

(+) 1 2

(+) :*: 1 :*: 2

+-- 2
|
+--+-- 1
   |
   +-- (+)

(+) 1 ((+) 2 3)

(+) :*: 1 :*: ((+) :*: 1 :*: 2)

+--+-- 3
|  |
|  +--+-- 2
|     |
|     +-- (+)
|
+--+-- 1
   |
   +-- (+)

3argfn 1 2 3

3argfn :*: 1 :*: 2 :*: 3

+-- 3
|
+--+-- 2
   |
   +--+-- 1
      |
      +-- 3argfn