Struct swipl::context::Frame

source ·

pub struct Frame { /* private fields */ }

Expand description

Context type for a prolog frame.

Examples

Discard a frame through dropping:

use swipl::prelude::*;
fn main() -> PrologResult<()> {
   // create a context
   let engine = Engine::new();
   let activation = engine.activate();
   let context: Context<_> = activation.into();

   let term = context.new_term_ref();

   {
       let frame = context.open_frame();
       term.unify(42_u64)?;
   }

   assert!(term.is_var());

   Ok(())
}

Discard a frame explicitely:

use swipl::prelude::*;
fn main() -> PrologResult<()> {
   // create a context
   let engine = Engine::new();
   let activation = engine.activate();
   let context: Context<_> = activation.into();

   let term = context.new_term_ref();

   let frame = context.open_frame();
   term.unify(42_u64)?;

   frame.discard();
   assert!(term.is_var());

   Ok(())
}

Close a frame:

use swipl::prelude::*;
fn main() -> PrologResult<()> {
   // create a context
   let engine = Engine::new();
   let activation = engine.activate();
   let context: Context<_> = activation.into();

   let term = context.new_term_ref();

   let frame = context.open_frame();
   term.unify(42_u64)?;
   let term2 = frame.new_term_ref();

   frame.close();
   assert_eq!(42_u64, term.get()?);
   // the following would result in a compile error:
   // term2.unify(42_u64)?;

   Ok(())
}

Rewind a frame:

use swipl::prelude::*;
fn main() -> PrologResult<()> {
   // create a context
   let engine = Engine::new();
   let activation = engine.activate();
   let context: Context<_> = activation.into();

   let term = context.new_term_ref();

   let frame = context.open_frame();
   term.unify(42_u64)?;

   let frame = frame.rewind();
   // term is a variable again so the following unification will succeed
   term.unify(43_u64)?;

   frame.close();
   assert_eq!(43_u64, term.get()?);

   Ok(())
}