A let expression let $\,\langle$ declList $\rangle\,$ in $\,\langle$ exp ${}_{1}$ $\rangle\,$ ; $\cdots$ ; $\,\langle$ exp ${}_{n}$ $\rangle\,$ end allows you to introduce local declarations that are valid only in expressions $\,\langle$ exp ${}_{1}$ $\rangle\,$ ; $\cdots$ ; $\,\langle$ exp ${}_{n}$ $\rangle\,$ . This expression is evaluated as follows.

1.

Each declaration in $\,\langle$ declList $\rangle\,$ is evaluated sequentially and adds the resulting environment to the current environment.
2.

Under the augmented environment, expressions $\,\langle$ exp ${}_{1}$ $\rangle\,$ ; $\cdots$ ; $\,\langle$ exp ${}_{n}$ $\rangle\,$ are evaluated in this order.
3.

The type and value of the last expression is those of this entire expression.

19.9 Local declaration expression let ⟨declList⟩ in ⟨exp1⟩;⋯;⟨expn⟩ end

19.9 Local declaration expression let $\,\langle$ declList $\rangle\,$ in $\,\langle$ exp ${}_{1}$ $\rangle\,$ ; $\cdots$ ; $\,\langle$ exp ${}_{n}$ $\rangle\,$ end