The BESM-6 Pascal compiler I'm experimenting with has a notable difference from Standard Pascal: formal arguments of formal parameters-procedures or functions are not specified, but are checked at runtime:
PASCAL COMPILER 15.0 (15.02.82) 00001 1 0 PROGRAM MAIN(OUTPUT); 00007 2 1 PROCEDURE P(FUNCTION F:INTEGER); 00007 3 3 BEGIN 00015 4 3 WRITELN(F(P)); 00036 5 2 END; 00037 6 1 FUNCTION F(I:INTEGER):INTEGER; 00037 7 3 BEGIN 00045 8 3 F := I + 5 00045 9 2 END; 00047 10 2 BEGIN 00050 11 2 P(F); 00072 12 0 END.
Here we pass an integer function
F to the procedure
P and we attempt to call it with a procedure argument, whereas it accepts an integer argument and returns it incremented by 5 (e.g. in case of
10 would be printed.
The compilation succeeds, and at runtime the following happens:
FORMAL PROC CALL ERROR FOR 1 PARAMETR CALL FROM 001032 PASCAL PM DUMP 9 STACK LENGTH. NAME= P.LINE=3 3586 STACK LENGTH. NAME= MAIN.LINE=12 PASCAL PMD END
I've been able to verify that actual parameters are checked for number and for "severe" type discrepancies. E.g. passing CHAR to a function which accepts INTEGER succeeds, but attempting to pass a procedure instead of an integer fails.
Standard Pascal would not accept the code as written; it requires the formal parameter prototypes to be declared the same way as in actual definitions, like
PROCEDURE P(FUNCTION F(I:INTEGER):INTEGER);
and all type checks are done at compile time.
Naturally, skipping compile-time type checks was done to reduce the size of the compiler at the cost of speed of the execution. Is it the way it was routinely done in the pre-standard Pascal compilers, or was it a corner cut specifically in the BESM-6 implementation? (A slight hint to the latter is the spelling error in the word PARAMETER which mirrors the Russian spelling ПАРАМЕТР.)