Implement MARKER

[ikysil]

https://forth-standard.org/standard/core/MARKER

MARKER
( "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.

Open points:

• restoring values of DEFERs
  • idea - redefine DEFER or IS

[ikysil]

• Trim list of wordlists
• Trim each wordlist
• Restore search XT for each wordlist (is it really needed?)
• Chain for markers, MARKER A executes actions of MARKER B if B was defined later
• Restore CONTEXT
• Restore CURRENT
• DP
• Restore user area pointer

[ikysil]

• Restore FORTH-RECOGNIZER