describe 'context' object

[kevinbarabash]

A context object would describe properties of identifiers that might affect how the AST might be manipulated. For instance A*B can be transformed to B*A if A and B are numbers. If they are matrices than the transform would be invalid because matrix multiplication is non-commutative.

Through the process of solving an equation, we may identify certain restrictions on the solutions, e.g. y = (x+1)/(x^2-1). Here x is a real number but x can't be -1 or 1.

Things to describe:

• value type: scalar, tuple, vector, matrix, etc.
• number type: real, complex, rational, integer, etc.
• constraints: list of Constraint objects (intervals, disallowed values, etc.)