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.