Structure

Instructions

Control Instructions

The set of recognised instructions is extended with the following:

$$\begin{array}{r}\begin{array}{llcl}& \mathit{instr}& ::=& \dots \\ & & |& \mathsf{try}\mathit{blocktype}{\mathit{instr}}^{\ast }(\mathsf{catch}\mathit{tagidx}{\mathit{instr}}^{\ast }{)}^{\ast }(\mathsf{catch}\mathsf{\_}\mathsf{all}{\mathit{instr}}^{\ast }{)}^{?}\mathsf{end}\\ & & |& \mathsf{try}\mathit{blocktype}{\mathit{instr}}^{\ast }\mathsf{delegate}\mathit{labelidx}\\ & & |& \mathsf{rethrow}\mathit{labelidx}\end{array}\end{array}$$

The instructions $\mathsf{try}$ and $\mathsf{rethrow}$, are concerned with exceptions. The $\mathsf{try}$ instruction installs an exception handler, and may either handle exceptions in the case of $\mathsf{catch}$ and $\mathsf{catch}\mathsf{\_}\mathsf{all}$, or rethrow them in an outer block in the case of $\mathsf{delegate}$.

The $\mathsf{rethrow}$ instruction is only allowed inside a $\mathsf{catch}$ or $\mathsf{catch}\mathsf{\_}\mathsf{all}$ clause and allows rethrowing the caught exception by lexically referring to a the corresponding $\mathsf{try}$.

When $\mathsf{try}$-$\mathsf{delegate}$ handles an exception, it also behaves similar to a forward jump, effectively rethrowing the caught exception right before the matching $\mathsf{end}$.