Functions and parameters

A function groups instructions under a name. Parameters receive its input values; RETURN sends a value back to the caller. This separates a calculation from input and output.

Declaration and call#

1FUNCTION sum(a, b)2  RETURN a + b3END4PRINT sum(7, 5)5result = sum(2, 9)6PRINT result

The program prints 12, then 11. In the first call, a receives 7 and b receives 5; the next call supplies new values. The argument count must match the parameter count.

Declare functions at the top level, outside other functions or blocks. Calls may appear before their declarations. User-defined function names are case-sensitive. Do not redefine built-in names such as LEN or ABS.

Local variables#

1x = 102FUNCTION double(x)3  x = x * 24  RETURN x5END6PRINT double(x)7PRINT x

The output is 20, then 10. Parameter x is local and does not overwrite the global variable with that name. Each call owns its variables. Functions can read globals, but an assignment inside a function creates or updates a local value. Caller-local variables are not visible to other functions.

Arguments are evaluated from left to right, exactly once. Scalar values are passed by value. Return and explicitly assign a result to use it outside the function.

RETURN and PRINT have different roles#

PRINT displays a value in the console. RETURN supplies it to another calculation and immediately exits the current function, even inside a loop or IF. Remaining instructions in that call do not run.

A function that returns no value can be called as a standalone instruction, but cannot be used in an expression. A bare RETURN has the same effect. RETURN outside a function raises an error.

Practice#

1. Write maximum(a, b) and test equal and negative arguments.
2. Write digitSum(n) using the digits lesson. For 4072, return 13.
3. Combine two calls in one expression. Continue with recursion.