SWI-Prolog -- portray

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

Pretty print a clause. A clause should be specified as a term `

<Head> 
:- <Body>

'. Facts are represented as `

<Head> 
:- true

' or simply <Head>. Variables in the clause are written as A, B, ... . Singleton variables are written as _. See also portray_clause/2.