Control statement

Control statements will be used to change the program flow of the HBasic program. A control statement may be a loop (while/loop/Until), an if-statement or a select statement.

<Control statement> ::=
    <If-statement> |
    <While-statement> |
    <Until-statement> |
    <do-statement> |
    <for-statement> |
    <select-statement>

<If-statement>::=
    If <condition> Then
        <statement-list >
    Else
        <statement-list>
    Else If
        <statement-list >
    End If

<while-statement> ::=
    While <condition> [Do]
        <statement-list>
    Wend

<Until-statement> ::=
    Until <condition> [Do]
        <statement-list>
    End Until

<For-statement> ::=
For loopvar = <expression> To <expression> [ Step <expression> ]
    <statement-list>
Next loopvar

<Do-statement> ::=
<Do-header>
    <statement-list>
<End-do-statement>

<Do-header> = Do |
    Do While <condition> |
    Do Until <condition>

<End-do-statement> ::= Loop |
    Loop While <condition> |
    Loop Until <condition>

<select-statement> ::=
    Select Case <expression>
        <case-list>
    End Case

<Case list> ::= { <Case statement> }

<Case statement> ::=
    Case <Expression> <statement-list> |
    Case Else <statement-list>

where "Case Else" should occure only once in the <case list> and should be the last statement in the list.

<condition> ::= <expression> |
    <Boolean-constant> |
    <expression> AND <expression> |
    <expression> OR <expression> |
    NOT <expression> |
    <expression> XOR <expression> |
    <expression> <bool-operator> <expression>

<Boolean-constant> ::= TRUE | FALSE

<bool-operator> ::= < | > | = | <> | <= | >=

Exit-statement

<Exit-statement> ::= Exit ( <number> )

The Exit statement may be used to terminate the program execution immediatly and return to the calling program. I have implemented the Exit statement to abort a running program if an error occured that cannot be solved by the program itself.