6.2.1850
MARKER
 
CORE EXT
 
( "<spaces>name" -- )

Skip leading space delimiters. Parse name delimited by a space. Create a definition for name with the execution semantics defined below.

name Execution:
( -- )

Restore all dictionary allocation and search order pointers to the state they had just prior to the definition of name. Remove the definition of name and all subsequent definitions. Restoration of any structures still existing that could refer to deleted definitions or deallocated data space is not necessarily provided. No other contextual information such as numeric base is affected.

See:
3.4.1 Parsing, 15.6.2.1580 FORGET, A.6.2.1850 MARKER.

Rationale:
As dictionary implementations have become more elaborate and in some cases have used multiple address spaces, FORGET has become prohibitively difficult or impossible to implement on many Forth systems. MARKER greatly eases the problem by making it possible for the system to remember "landmark information" in advance that specifically marks the spots where the dictionary may at some future time have to be rearranged.