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 withuntil
is used to surround the loop body of a tail-controlled loop. It is the only frame type not ending with anend
.- 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 propertry
is illegal).
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.
begin
- If there is no need for a
finalization
part,initialization
can be replaced bybegin
.
- 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 inasm
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.