-- BBContext.mesa
-- Russ Atkinson, October 26, 1982 1:27 pm

DIRECTORY
  Rope USING [ROPE],
  RTBasic USING [TV],
  WorldVM USING [World];
    
BBContext: CEDAR DEFINITIONS
  = BEGIN OPEN Rope, RTBasic, WorldVM;

  Context: TYPE = REF ContextRep;
  ContextRep: TYPE = PRIVATE RECORD
    [world: World _ NIL,
     headLF: TV _ NIL,
     headGF: TV _ NIL,
     active: BOOL _ TRUE
     ];

  ContextForLocalFrame: PROC [lf: TV] RETURNS [Context];
    -- returns context for the given local frame
    -- the world and gf components are inherited

  ContextForGlobalFrame: PROC [gf: TV] RETURNS [Context];
    -- returns context for the given global frame
    -- the world component is inherited

  ContextForWorld: PROC [world: World] RETURNS [Context];
    -- returns context for the given world
    -- the gf and lf components will be null

  GetContents: PROC [context: Context] RETURNS [world: World, gf,lf: TV];
    -- atomic proc to examine a world
    -- will return all NILs if the context is no longer active

  DestroyContext: PROC [context: Context];
    -- invalidates the given context (unless it is the default context)

  ActionContinuation: TYPE = {continue, quit};

  FrameAction: TYPE = PROC [lf: TV] RETURNS [ActionContinuation _ continue];
    
  EnumerateFramesInContext: PROC [context: Context, action: FrameAction];

  StackSearch: PROC
     [context: Context, name: ROPE, case: BOOL _ TRUE, depth: INTEGER _ 100]
     RETURNS [gf,lf,tv: TV];
     -- search stack starting at startLF for named variable
     -- if case is true then case of variable name matters
     -- if lf = NIL and gf = NIL then variable was not found
     -- if gf # NIL then variable was in global frame
     -- if lf # NIL then variable was in local frame
     -- we will not look more than depth levels in the stack
     
  GlobalFrameSearch: PROC
       [context: Context, frameName,itemName: ROPE _ NIL, case: BOOL _ TRUE]
       RETURNS [gf, tv: TV];
       -- context = NIL => use the default
       -- itemName = NIL => just search for the global frame named by frameName
       -- case = FALSE => ignore case of global frame

  RecordSearch: PROC
     [record: TV, name: ROPE, case: BOOL _ TRUE]
     RETURNS [base, tv: TV];
     -- search record for named component (auto-dereferencing)
     -- base # NIL => tv is OK
     -- base = NIL => component not found 

  SetDefaultGlobalContext: PROC [context: Context] RETURNS [ROPE];
    -- set the default global context for searching
    -- returns NIL if successful, error msg if not
  
  GetDefaultGlobalContext: PROC RETURNS [Context];
    -- returns the default global frame tv
  
  FindMatchingGlobalFrames: PROC
      [world: World, pattern: ROPE _ NIL, action: FindAction];
      -- enumerates the gf,tv pairs with names that match (*-matching)
      -- names given by gfn and tvn
      -- if action[gf,tv,name] = quit, then stop

  FindAction: TYPE = PROC [gf: TV, name: ROPE] RETURNS [ActionContinuation _ continue];
    -- type of proc used to process matching global frames

  IsStarted: PROC [gf: TV] RETURNS [BOOL];

  END.