Subcall Datatypes IN v.s. IO

[vmaddur]

Title says it all! I was wondering what the difference between "IN_16" vs "IO_16" was with respect to subcall parameters. Could you clarify this?

[dlech]

IO means the parameter is both an input (IN) parameter and an output (OUT) parameter.

Input parameters are set to the value that is passed into CALL when the subcall starts. Output parameters set the variable passed to CALL when the subcall return. So IO does both.

vmthread {
    DATA16 x
    MOVE16(5,x)
    // x has value of 5
    CALL(AddOne,x)
    // x still has value of 5
}

subcall AddOne {
    IN_16 n
    // n has value of 5
    ADD16(n,1,n)
    // n has value of 6
}

vmthread {
    DATA16 x
    MOVE16(5,x)
    // x has value of 5
    CALL(AddOne,x)
    // x has value of 1
}

subcall AddOne {
    OUT_16 n
    // n has value of 0
    ADD16(n,1,n)
    // n has value of 1
}

vmthread {
    DATA16 x
    MOVE16(5,x)
    // x has value of 5
    CALL(AddOne,x)
    // x has value of 6
}

subcall AddOne {
    IO_16 n
    // n has value of 5
    ADD16(n,1,n)
    // n has value of 6
}