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===Procedure declarations===
Procedures were implemented in a fashion similar to the [[C programming language]], with the return type, if any, in front of the name, for instance, {{code|STRING PROCEDURE toUpper(STRING originalStr);BEGIN...|pascal}}. Note the uncommon use of the semicolon here, whereas Pascal would immediately follow with a block, typically a {{code|BEGIN}}.{{sfn|Smith|1976|p=21}}
In order to improve performance, SAIL added two procedure qualifiers, {{code|SIMPLE}} and {{code|RECURSIVE}}. {{code|RECURSIVE}} told the compiler that the procedure might call itself, and thus its [[local variable]]s had to be written to the stack, not just the subroutine return information. {{code|SIMPLE}} did the opposite, demanding the procedure have no local variables at all, not allowing {{code|GOTO}} out of the function, and could not refer to enclosing procedure's variables. These directives could avoid the requirement of filling out a complete [[activation record]], thereby improving performance.{{sfn|Smith|1976|p=22}} This also had the side-effect of meaning that variables declared within a procedure that was not marked {{code|RECURSIVE}} would not be reset between calls,{{sfn|Smith|1976|p=22}} acting similar to C's {{code|static}}.
SAIL also included the {{code|FORWARD}} qualifier, used to insert [[forward declaration]]s, typically when two procedures call each other.{{sfn|Smith|1976|p=21}} {{code|RETURN}} worked as in C, exiting the procedure and returning to the caller, as well as optionally returning a value if the procedure uses one.{{sfn|Smith|1976|p=23}} Parameters passed to the procedures could be by {{code|VALUE}} or {{code|REFERENCE}}, the later allowing values to be passed back.{{sfn|Smith|1976|p=24}}
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