Package code.instr

This package abstracts the instructions of the functional logic virtual machine.

See:
Description

Interface Summary

Instruction

Interface of all the instructions of the virtual machine.

Class Summary

Branch	Execute a goto -like instruction of the virtual machine code.
Choice	Execute a non-deterministic step.
Fail	Fail the current computation.
Load	Load in the machine register a subterm of the top of the pre-redex stack.
MakeAnon	Construct a fresh (anonymous) variable and push it on the pre-term stack.
MakeChar	Construct a character term and push it on the pre-term stack.
MakeFloat	Construct an float term and push it on the pre-term stack.
MakeInt	Construct an integer term and push it on the pre-term stack.
MakePartial	Construct a term from a (root) symbol partially applied to a bunch of arguments.
MakeRef	Construct a term that wraps a variable.
MakeTerm	Construct a term from a (root) symbol and a bunch of arguments.
MakeVar	Push on the stack an uninstantiated free variable stored in some register of variables.
Narrow	Narrow the top term of the pre-term stack.
Pop	Move the top term of the pre-term stack (which is popped) in the register.
Push	Push the register on the pre-term stack.
Replace	Replace the top of the pre-redex stack with the register.
Residuate	Residuate the current computation.
StoreVar	Store a fresh uninstantiated variable in a register

Package code.instr Description

This package abstracts the instructions of the functional logic virtual machine. The machine executed code consisting of an array of instructions.

Currently (Fri Jan 24 14:22:57 PST 2003) the instructions are represented by Java objects. An instruction is generated by calling its constructor. There is no provision (yet) to read instructions from a stream.

Some instructions refer to Symbols of a source functional logic program. These symbols are represented by string when they occur as arguments of an instruction's constructor. The same symbols are represented by integer in the constructor object to ensure fast access to a symbol information.

The representation of instructions as object is potentially inefficient, but excellent for prototyping. There are no specific classes for the functional logic virtual machine. Rather, each instruction defines an execute method, dispatched by virtual polymorphism, which perform the computation intended by the instruction. This allows the programmer to add/replace/delete each instruction independently of any other instruction.

An instruction is executed within the context of a Computation. A computation has the following main elements:

• A pre-redex stack containing needed positions (subterms actually),
• A pre-term stack used to build terms from simpler terms,
• A register for comparing terms and for moving them to and from the term stack.