SWI-Prolog -- xref

Availability::- use_module(library(prolog_xref)).(can be autoloaded)

[nondet]xref_called(?Source, ?Called, ?By)

[nondet]xref_called(?Source, ?Called, ?By, ?Cond)

[nondet]xref_called(?Source, ?Called, ?By, ?Cond, ?Line)

True when By is called from Called in Source. Note that xref_called/3 and xref_called/4 use distinct/2 to return only distinct Called-By pairs. The xref_called/5 version may return duplicate Called-By if Called is called from multiple clauses in By, but at most one call per clause.

`By`	is a head term or one of the reserved terms `'<directive>'(Line)` or `'<public>'(Line)`, indicating the call is from an (often initialization/1) directive or there is a public/1 directive that claims the predicate is called from in some untractable way.
`Cond`	is the (accumulated) condition as defined by `:- if(Cond)` under which the calling code is compiled.
`Line`	is the start line of the calling clause.