Delayed/Conditional Substitution

[cheuberg]

Mathematica (see http://reference.wolfram.com/language/ref/RuleDelayed.html) has a very useful feature called delayed rule. Instead of a static rule, a function is invoked which decides looking at the argument how the actual substitution should be carried out. This is a useful feature when simplifying some symbolic expressions.

This ticket shall implement such a delayed substitution in SageMath.

CC: @dkrenn @behackl @rwst

Component: symbolics

Author: Clemens Heuberger

Branch/Commit: 224476e

Reviewer: Daniel Krenn, Ralf Stephan

Issue created by migration from https://trac.sagemath.org/ticket/24773

[cheuberg]

Branch: u/cheuberg/delayed-substitution

[cheuberg]

Commit: 5581894

[cheuberg]

New commits:

0f55981	Trac #24773: delayed substitution: first version
b801825	Trac #24773: remove input argument self
6d0793a	Trac #24773: Shorten references
5581894	Trac #24773: Fix see also block

[dkrenn]

comment:3

LGTM, but I want to raise the following to be discussed: the name delayed_substitution of the method. The other substitute-methods are called substitute*, so maybe an substitute_delayed would fit more into this scheme. However, I do not have a strong opinion on this topic.

The first basic Mathematica example is

{x, x, x} /. x :> RandomReal[]

so maybe adding this example as well could be a benefit.

[dkrenn]

Reviewer: Daniel Krenn

[rwst]

comment:4

Replying to @dkrenn:

LGTM, but I want to raise the following to be discussed: the name delayed_substitution of the method. The other substitute-methods are called substitute*, so maybe an substitute_delayed would fit more into this scheme.

Agree, mostly because it makes it easier to be found by TAB completion.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

d2b835c

Trac #24773: delayed_substitution -> substitution_delayed

[sagetrac-git]

Changed commit from 5581894 to d2b835c