Jumps and subroutines

Older code moves around with labels: goto to a label, on n goto to the nth of a list, and gosub to a subroutine that returns. tiko keeps the first two and refuses the third.

gosub belongs to the older dialects:

'' GOSUB jumps to a label; RETURN comes back. tiko refuses it.
dim as long total = 0
gosub add_one
gosub add_one
print total
end

add_one:
    total = total + 1
    return

gosub.bas(3,7): error TKO0409: 'GOSUB' is not available in the fb dialect
     |
   3 | gosub add_one
     |       ^
gosub.bas(4,7): error TKO0409: 'GOSUB' is not available in the fb dialect
     |
   4 | gosub add_one
     |       ^

A gosub subroutine has no parameters and no local variables: everything it touches is shared with its caller. Rewritten as a sub, the variable it changes becomes a byref parameter:

'' The subroutine as a sub: what it changes is passed byref.
sub AddOne( byref total as int32 )
    total += 1
end sub

dim as int32 total = 0
AddOne( total )
AddOne( total )
print total

Output

 2

on … goto still compiles:

'' ON n GOTO jumps to the n-th label in its list. tiko accepts it.
for choice as long = 0 to 4
    print "choice"; choice; ": ";
    on choice goto add, list, quit
    '' Out of range -- 0, or past the end of the list -- falls through.
    print "no such option"
    goto next_choice
add:
    print "adding a record"
    goto next_choice
list:
    print "listing the records"
    goto next_choice
quit:
    print "quitting"
next_choice:
next

Output

choice 0: no such option
choice 1: adding a record
choice 2: listing the records
choice 3: quitting
choice 4: no such option

A value of 0, or one past the end of the list, jumps nowhere, and execution carries on with the next line. In modern code, select case says the same thing with no labels and no goto at the end of every branch:

'' The same menu with select case: no labels, no jumps.
for choice as int32 = 0 to 4
    print "choice"; choice; ": ";
    select case choice
    case 1
        print "adding a record"
    case 2
        print "listing the records"
    case 3
        print "quitting"
    case else
        print "no such option"
    end select
next

Output

choice 0: no such option
choice 1: adding a record
choice 2: listing the records
choice 3: quitting
choice 4: no such option

Other older statements are refused the same way, each with TKO0409 naming the keyword: resume, let in front of an assignment, call in front of a call, the def statements such as defint, and option statements. Numbered lines are refused too; a label is a name followed by a colon on a line of its own.

Activities

1. Add a fourth option to both menus and compare how much each one changed.
2. Make AddOne take the amount to add as a second parameter.