A loop statement specifies the repeated execution of a statement sequence. It is terminated by the execution of any exit statement within that sequence.

   LoopStatement = LOOP StatementSequence END.

Example:

   LOOP
     IF t1^.key > x THEN
        t2 := t1^.left; p:= TRUE
     ELSE
        t2 := t1^.right; p:= FALSE
     END;
     IF t2 = NIL THEN
        EXIT
     END;
     t1=t2
   END

While, repeat, and for statements can be expressed by loop statements containing a single exit statement. Their use is recommended as they characterize the most frequently occurring situations where termination depends either on a single condition at either the beginning or end of the repeated statement sequence, or on reaching the limit of an arithmetic progression. The loop statement is, however, necessary to express the continuous repetition of cyclic processes, where no termination is specified. It is also useful to express situations exemplified above. Exit statements are contextually, although not syntactically bound to the loop statement which contains them.

Source:

Wirth N: Programming in Modula-2, 3rd ed. Springer Verlag, Berlin, 1985.