Frame

A frame (frequently also referred to as block) is a language construct grouping a (possibly empty) sequence of statements (or instructions in the case of asm frames).

available types

All frames but repeat … until are terminated by the word end. Frame types are distinguished by their corresponding opening words.

• Pascal: These frames expect Pascal statements or may contain other frames. begin
  This frame begins a (possibly empty) sequence of statements. In the context of routine definitions or a program it can delimit a scope.

  else/otherwise
  This frame surrounds a “catch-all”-alternative as part of a case statement.

  repeat … until
repeat in conjunction with until is used to surround the loop body of a tail-controlled loop. It is the only frame type not ending with an end.

  exception treatment
  If exceptions are supported in the current compiler mode, the following frames are available as well. These frames are in fact “double”-frames: They group two sequences at once. Neither of them can be used independently (e. g. writing finally … end; without a proper try is illegal).

  try … except …
  Use this to install exception handlers.

  try … finally …
  Use this to ensure a certain code fragment is executed despite any thrown exceptions.

  unit overhead

  :; initialization … finalization

  This double-frame designates code being executed when the corresponding unit is loaded or unloaded. Either part of this frame is optional. This frame may also delimit a scope.

• Assembly language: Frames beginning with asm expect assembly language. In pure assembly routines, this kind of frame may delimit a scope, too. Note, you cannot nest other frames in asm frames.

style

Although not mandatory, it is customary to indent all code surrounded by frame markers by one level.

try
    openJar;
except
    throwATantrum;
end;

Some styles add another indentation level for nested or subordinate frame markers per se.

if apples = oranges then
  begin
    protest;
    halt(123);
  end;

As you can see from the examples above, it is customary to put frame delimiters isolated in their own line. Exempt of this guideline are of course frames accepting or requiring additional clauses to be syntactically complete:

repeat
    write('Enter a non-negative integer: ');
    readLn(i);
until i >= 0;

asm
    rdrand eax
    mov n, eax
END ['eax'];

technical background

Frames frequently, but not always, turn up to be (conditional) jmp targets. Some compile-time optimizations require code to be structured in a certain way, frames setting boundaries for that.

From the Free Pascal wiki, page "Frame", as it stood on 2021-02-06 after a change by Kai Burghardt, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.