ebnf - 無限ループまたは if ステートメントの Forth 言語 EBNF ルール

Question

Forth 無限ループまたは if ステートメントを記述するEBNFルールはありますか?

Answer 1

EBNF is used to describe syntax. A loop being infinite or otherwise wouldn't normally fall within what it would describe. As such, you'd be looking at the EBNF for an indefinite loop, which looks something like:

indefinite_loop ::= 'BEGIN' statements cond 'UNTIL'

Normally the cond will be something that pushes a 0 or 1 on the stack to determine whether to continue the loop (0 means continue the loop, 1 means exit). As such, if you just insert a 0 directly, the loop will execute forever:

: infinite_loop BEGIN do_whatever 0 UNTIL ;

Answer 2

以下も使用できます。

infinite_loop ::= 'BEGIN' statements 'AGAIN'

このAGAIN単語は、無条件分岐を に戻すために使用されますBEGIN。例えば：

: main-loop BEGIN listen-for-event process-event AGAIN ;