AbstractExpression

class pqp.symbols.AbstractExpression

Bases: AbstractMath, ABC

Abstract class defining needed recursive operations for relations

Methods Summary

assign(var[, val])	Assigns a value to a variable in an expression.
copy()	Returns a copy of the expression (variables are not copied).
free_variables()	Returns the set of free variables in an expression.
intervene(var)	Intervenes on a variable in an expression.
r_adapt_map(func)	Recursive map where the func decides callables used to transform children
r_map(func)	Recursively maps a function over the expression tree
sorted()	Returns a sorted copy of an expression for structural comparison.
syntactic_eq(other)	Test whether two Expressions are syntactically identical (structural compare without sorting first)

Methods Documentation

assign(var, val=None)

Assigns a value to a variable in an expression.

Note that assignment will not propogate downwards through a sum over a variable.

Parameters:

• var (Variable) – The variable to assign to

• val (AbstractMath) – The value to assign, if this is P.unassigned, the expression is copied and returned

Returns:

a new expression where the assignment has occured

Return type:

AbstractExpression

abstract copy()

Returns a copy of the expression (variables are not copied).

free_variables()

Returns the set of free variables in an expression.

intervene(var)

Intervenes on a variable in an expression.

Note that intervention will not propogate downwards through a sum over a variable.

Parameters:

var (Variable or list) – The variable(s) to intervene on

Returns:

a new expression where the intervention has occured

Return type:

AbstractExpression

abstract r_adapt_map(func)

Recursive map where the func decides callables used to transform children

DO NOT USE! This is a powerful and necessary method but it results in almost unreadable code.

So, func takes an AbstractExpression and needs to return a tuple of two things. First, a function A which maps from AbstractExpression to AbstractExpression. Second, a function B of the same time as func.

At each level of recursion, func will be called on an expression E to get A and B. This method, r_adapt_map will then be called on the children of E with B as input (if B is None, recursion terminates). An expression of the same type as E is then constructed with the results of the recursive calls using B, and A is applied to the result.

Parameters:

func (function) – A function that takes an AbstractExpression and returns two functions (see desc)

abstract r_map(func)

Recursively maps a function over the expression tree

abstract sorted()

Returns a sorted copy of an expression for structural comparison.

abstract syntactic_eq(other)

Test whether two Expressions are syntactically identical (structural compare without sorting first)