Program statements

DIM name (dim1, dim2, …, dimK)

DIM ("dimension") is a statement that provides a short cut to creating roArray objects. It sets variable name to type "roArray", and creates Arrays of Arrays as needed for multi-dimensional arrays. The dimension passed to Dim is the index of the maximum entry to be allocated (the array initial size = dimension+1); the array will be resized larger automatically if needed.

Dim array[5]

Is the same as:

array=CreateObject("roArray",6,true)

Note that x[a,b] is the same as x[a][b].

 Dim c[5, 4, 6]
 For x = 1 To 5
    For y = 1 To 4
        For z = 1 To 6
            c[x, y, z] = k
            k = k + 1
        End for
    End for
 End for


 k=0
 For x = 1 To 5
    For y = 1 To 4
        For z = 1 To 6
            If c[x, y, z] <> k Then print"error" : Stop
            If c[x][y][z] <> k Then print "error": Stop
            k = k + 1
        End for
    End for
 End for

variable = expression

Assigns a variable to a new value.

Example

a$="a rose is a rose"
b1=1.23
x=x-z1

In each case, the variable on the left side of the equals sign is assigned the value of the constant or expression on the right side.

END

Terminates execution normally.

STOP

Interrupts execution return a STOP error. Invokes the debugger. Use "cont" at the debug prompt to continue execution, or "step" to single step.

GOTO label

Transfers program control to the specified line number. GOTO label results in an branch. A label is an identifier terminated with a colon, on a line by itself.

For example:

mylabel:
print "Anthony was here!"
Goto mylabel

RETURN [expression]

Used to return from a function back to the caller. If the function is not of type Void, return can return a value to the caller.

FOR counter = exp TO exp [STEP exp] / END FOR

Creates an iterative (repetitive) loop so that a sequence of program statements may be executed over and over a specified number of times. The general form is (brackets indicate optional material):
FOR counter-variable = initial value TO final value [STEP increment]
[program statements]
END FOR
In the FOR statement, initial value, final value and increment can be any expression. The first time the FOR statement is executed, these three are evaluated and the values are saved; if the variables are changed by the loop, it will have no effect on the loop's operation. However, the counter variable must not be changed or the loop will not operate normally. The first time the FOR statement is executed the counter is set to the "initial value" and to the type of "initial value".
At the top of the loop, the counter is compared with the final value specified in the FOR statement. If the counter is greater than the final value, the loop is completed and execution continues with the statement following the END FOR statement. (If increment was a negative number, loop ends when counter is less than final value.) If the counter has not yet exceeded the final value, control passes to the first statement after the FOR statement.
When program flow reaches the END FOR statement, the counter is incremented by the amount specified in the STEP increment. (If the increment has a negative value, then the counter is actually decremented.) If STEP increment is not used, an increment of 1 is assumed.

For example:

For i=10 To 1 Step -1
    print i
End For

"EXIT FOR" is used to exit a FOR block prematurely.

FOR EACH item IN object

The FOR EACH statement iterates through each item in any object that has an "ifEnum" interface (enumerator). The For block is terminated with a END FOR statement. The variable item is set at the top of the loop to the next item in the object. Objects that are intrinsically ordered (like a List) are enumerated in order. Objects that have no intrinsic order (like AssociativeArray) are enumerated in apparent random order. It is okay to delete entries as you enumerate them.

"EXIT FOR" is used to exit a FOR block prematurely.
The following objects can be enumerated: roList, roArray, roAssociativeArray, roMessagePort.

For example:

aa = { joe: 10, fred: 11, sue:9 }

For Each n In aa
    Print n;aa[n]
    aa.delete(n)
End For

WHILE expression / EXIT WHILE / END WHILE

The While loop executes until expression is false. The "exit while" statement can be used to terminate a while loop prematurely.

For example:

k = 0
while k = 0
    k = 1
    print "loop once".
end while

while true
    print "loop once"
    if k <> 0 then exit while
end while

CONTINUE FOR / CONTINUE WHILE

The "continue" statement terminates the execution of the statements in the current iteration of the loop, and continues execution of the loop with the next iteration

For example:

fruits = ["orange", "lemon", "lime"]
for each fruit in fruits
    if fruit = "lemon" then continue for
    ? fruit
end for
...
counter = 0
while counter < 3
    if counter = 1 then
        counter++
        continue while
    end if
    ? counter
    counter++
end while

TRY / CATCH variable / END TRY

Use to trap exceptions, which enables the implementation of error handling in BrightScript programs. Schematically, the syntax is as follows:

TRY
    ' Zero or more statements ("TRY block")
CATCH exception_object_variable_name
    ' Zero or more statements ("CATCH block")
END TRY

END TRY and ENDTRY are equivalent

The TRY block of statements is executed. If and only if an error occurs, the CATCH block of statements is executed, and the named variable is assigned the information about the triggering exception. If no error occurs during execution of the TRY block, the CATCH block is skipped.

It is illegal to put a GOTO label within a TRY block (i.e., between TRY and CATCH). A GOTO label may exist exist between CATCH and END TRY, however.

The variable name specified as the exception object in the CATCH clause must refer to a simple variable. It cannot be an array element, for example. The following are not legal as exception object references in the CATCH clause:

CATCH                ' no object variable at all -- an object must always be specified
CATCH someArray[23]  ' array element is bad exception object
CATCH bill.ted       ' object field is bad exception object
CATCH 22             ' literal constant is bad exception object
CATCH a+wave         ' expression is bad exception object

Information about the exception is contained within an exception object that is assigned to the CATCH-clause variable. This exception object can contain the following elements:

A backtrace is an array of associative arrays, each of which includes at least the following elements:

Example code

The following example sends an error message, including the contents of the exception record, to the debug console.

TRY
    PRINT 1/0
CATCH e
    PRINT "Division failed: ", e
END TRY

TRY and CATCH are not keywords in BrightScript. Programmers should treat them as reserved identifiers and avoid using them. In particular, legacy code that may already employ them as ordinary identifiers should be rewritten to use different identifiers instead.

TRY and CATCH were introduced into BrightScript with Roku OS version 9.4, and any app that uses them must declare a minimum OS version of 9.4 in the Package Upload Developer Dashboard page during app submission.

Nested TRY/CATCH statements

TRY/CATCH statements can be nested within TRY or CATCH blocks, as needed. Here is an example:

PRINT "Starting"
x = "I'm not an array"
TRY
    PRINT "x[0]*2=";x[0]*2
CATCH e
    TRY
        PRINT "I think that failed because ";x[0];" isn't a number"
    CATCH e
        PRINT "Nope, I guessed wrong: ";e.message
    END TRY
END TRY
PRINT "Ending"

The STOP statement produces an uncatchable error, consistent with its intended use in debugging.

THROW expression

Use the THROW statement to propagate an exception back to the caller of the present code.

The expression given in the THROW statement should evaluate to an exception object (or the equivalent associative array), as defined for TRY/CATCH. A single String is also acceptable as operand, however. In that case, BrightScript creates a default exception object, fills the message field with the supplied String, and sets the error number to ERR_USER (&h28).

THROW is a keyword in BrightScript.

THROW was introduced into BrightScript with Roku OS version 9.4, and any app that uses it must declare a minimum OS version of 9.4 in the Package Upload Developer Dashboard page during app submission.

Example code

FUNCTION reciprocal(x)
    RETURN 1/x
END FUNCTION

FUNCTION factorial(n)
    IF n < 0 THEN
        THROW "Cannot calculate negative factorial."
    ELSE IF n = 0 THEN
        RETURN 1
    ELSE
        RETURN n * factorial(n-1)
    END IF
END FUNCTION

SUB main()
    TRY
        PRINT reciprocal(0)
    CATCH e
        PRINT "reciprocal() failed: ", e.message
    END TRY

    PRINT factorial(-2) ' Error will be reported by BrightScript runtime/debugger
END SUB

REM

Instructs the compiler to ignore the rest of the program line. This allows you to insert comments (REMarks) into your program for documentation. An ' (apostrophe) may be used instead of REM.

For example:

Rem ** this remark introduces the program **
' this too is a remark

IF expression THEN statements [ELSE statements]

There are two forms of the IF THEN ELSE statement. The single line form (this one), and the multi-line or block form (see next section). The IF instructs the Interpreter to test the following expression. If the expression is true, control will proceed to the statements immediately following the expression. If the expression is False, control will jump to the matching ELSE statement (if there is one) or down to the next program line.

For example:

if x > 127 then print "out of range"
If caveman = "fred" then print "flintstone" else print "rubble"

THEN is optional in the above and similar statements.

Block IF, ELSEIF, THEN, ENDIF

The multi-line or block form of IF THEN ELSE is more flexible. It has the form:

 if BooleanExpression then
   statements
 elseif BooleanExpression then
   statements
 else
   statements
 end if

There may be any number of elseif statements, or there may be none. The else statement may also be omitted. "elseif" can also be written as two words: "else if".

For example:

msg = wait(0, p)
if type(msg) = "roVideoPlayerEvent" then
    if debug then print "video event"
    if msg.isFullResult()
        if debug then print "video finished"
        return 9
    end if
else if type(msg) = "roUniversalControlEvent" then
    if debug then print "button press "; msg.GetInt()
    HandleButton(msg.GetInt())
elseif msg = invalid then
    if debug print "timeout"
    return 6
end if

PRINT item list

Prints an item or a list of items on the console. The items may be either strings, number, variables, or expressions. Objects that have an ifInt, ifFloat, or ifString interface may also be printed.

The items to be PRINTed may be separated by commas or semi-colons. If commas are used, the cursor automatically advances to the next print zone before printing the next item. If semi-colons are used, no space is inserted between the items printed.

Positive numbers are printed with a leading blank (instead of a plus sign); floating point numbers are printed with a trailing blank; and no blanks are inserted before or after strings.

For example:

x=5:print 25; " is equal to"; x^2
 25 is equal to 25

a$="string":print a$;a$,a$;" ";a$
stringstring    string string

print "zone 1","zone 2","zone 3","zone 4"
zone 1          zone 2          zone 3          zone 4

? is a short cut for the print statement. For example:

x=5:? 25; " is equal to"; x^2

Each print zone is 16 char wide. The cursor moves to the next print zone each time a comma is encountered.

print "print statement #1 "; "print statement #2"

Output: print statement #1 print statement #2

Semi-colons can be dropped in some cases. For example, this is legal:

Print "this is a five " 5 "!!"

A trailing semi-colon over-rides the cursor-return so that the next PRINT begins where the last one left off. If no trailing punctuation is used with print, the cursor drops down to the beginning of the next line.

A few examples of printing enumerable objects:

Printing Enumerable Objects

Print {}
' this will print: <Component: roAssociativeArray> =  { }

Print {a:1}
' this will print: <Component: roAssociativeArray> =  { a: 1 }

Print []
' this will print: <Component: roArray> = [ ]

Print [5]
' this will print: <Component: roArray> = [ 5 ]

TAB (expression)
Moves the cursor to the specified position on the current line (modulo the width of your console if you specify TAB positions greater than the console width). TAB may be used several times in a PRINT list.

print tab(5)"tabbed 5";tab(25)"tabbed 25"

No punctuation is required after a TAB modifier. Numerical expressions may be used to specify a TAB position. TAB cannot be used to move the cursor to the left. If the cursor is beyond the specified position, the TAB is ignored.

POS ( x )
Returns a number from 0 to window width, indicating the current cursor position on the cursor. Requires a "dummy argument" (any numeric expression).

print tab(40) pos(0) 'prints 40 at position 40
print "these" tab(pos(0)+5)"words" tab(pos(0)+5)"are"; tab(pos(0)+5)"evenly" tab(pos(0)+5)"spaced"

FUNCTION([parameter [= default] AS type, …]) AS type / END FUNCTION

A function is declared using the function statement. In parentheses, one or more optional parameters to be passed may be declared. The return type of the function may also be declared. If the parameter or return type are not declared, they are assumed to be "dynamic" Intrinsic types are passed by value (a copy is made). Objects are passed by reference. Parameters can be of type:

• Integer
• Float
• Double
• Boolean
• String
• Object
• Dynamic
• Function

In addition to the above types, the return type can be:

• Void

Each parameter can have a default value, which is used if the parameter is not included in the call. The default parameter is declared by following the parameter name with an equal sign and the default value. If any parameter has a default value, then each following parameter must also have a default value. In the following examples, the functions add2 and add3 can be called with either one or two parameters.

For example:

Function cat(a, b)
    Return a+b 'a, b could be numbers or strings
End Function

Function five() as Integer
    Return 5
End function

Function add(a as Integer, b as Integer) As Integer
    Return a+b
End function


Function add2(a as Integer, b=5 as Integer) As Integer
    Return a+b
End Function


Function add3(a as Integer, b=a+5 as Integer) as Integer
    Return a+b
End Function

Functions have their own scope.

The statement "Sub" can be used instead of "function" as a shortcut to a function of Void return Type.

If a function is called from an associative array, then a local variable "m" is set to the AssociativeArray that the function is stored in.

For example:

Sub main()
    obj={
        add: add
        a: 5
        b: 10
    }

    obj.add()
    print obj.result
End Sub


Function add() as void
    m.result = m.a + m.b
End Function

If a function is not called from an AssociativeArray, then its "m" is set to an AssociativeArray that is global to the module, and persists across calls.

Anonymous functions

A function is anonymous if it does not have a name. Note that Anonymous Functions do not currently create closures. An Anonymous Function can be declared like this:

myfunc = Function (a, b)
    Return a+b
End Function

print myfunc(1,2)

They can be used with associative array literals like this:

q = {
    starring : Function(o, e)
        str = e.GetBody()
        print "Starring: " + str
        toks = box(str).tokenize(",")
        For Each act In tok
            actx = box(act).trim()
            If actx <> "" Then
                print "Actor: [" + actx + "]"
                o.Actors.Push(actx)
            End If
        End For
        Return 0
    End Function
}

q.starring(myobj, myxml)