Glossary

acode

An intermediate representation of Lisp code produced by the compiler front-end. Short for "alphatized code", meaning "has undergone alpha reduction", which in turn means "all lambda-bound variables have been consistently renamed".

dnode

Two native words. Lisp heap memory is allocated in units of dnodes.

gvector

A uvector whose elements are nodes.

immediate

A value in memory or a register that is a raw, untagged value.

ivector

A uvector whose elements are immediates.

node

A value in memory or a register that is a tagged lisp datum.

punt, puntable

If a variable is bound to a simple expression and is never setq'd, then all references to the variable can be replaced by references to the simple expression in question. This process is called "punting".

tagged return address

On x86, the call instruction unconditionally pushes a return address onto the stack. The compiler aligns the call instruction (via insertion of nop instructions) such that the pushed return address will have a special tag that the GC can recognize.

uuo

An "unimplemented user operation". Sometimes called a trap (after the PowerPC instructions). An illegal instruction used as a way for lisp code to request service from the lisp kernel (such as allocate more memory, initiate a GC, and so forth).

uvector

A memory-allocated object with a header word that describes the object's type and the number of elements it contains. (The name comes from Spice Lisp.)

value stack

A stack that contains tagged lisp objects (nodes) such as function arguments, local variables, and other stack-allocated lisp objects. The contents of the value stack between its bottom and top are always unambiguously nodes.