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cppdraft/exec/stopped/err.md

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+[exec.stopped.err]
+
+# 33 Execution control library [[exec]](./#exec)
+
+## 33.9 Senders [[exec.snd]](exec.snd#exec.stopped.err)
+
+### 33.9.12 Sender adaptors [[exec.adapt]](exec.adapt#exec.stopped.err)
+
+#### 33.9.12.15 execution​::​stopped_as_error [exec.stopped.err]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4856)
+
+stopped_as_error maps an input sender's stopped completion operation
+into an error completion operation as a custom error type[.](#1.sentence-1)
+
+The result is a sender that never completes with stopped,
+reporting cancellation by completing with an error[.](#1.sentence-2)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4862)
+
+The name stopped_as_error denotes a pipeable sender adaptor object[.](#2.sentence-1)
+
+For some subexpressions sndr and err,
+let Sndr be decltype((sndr)) and
+let Err be decltype((err))[.](#2.sentence-2)
+
+If the type Sndr does not satisfy [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]") or
+if the type Err does not satisfy [*movable-value*](exec.general#concept:movable-value "33.1 General [exec.general]"),stopped_as_error(sndr, err) is ill-formed[.](#2.sentence-3)
+
+Otherwise, the expression stopped_as_error(sndr, err) is expression-equivalent to:transform_sender(*get-domain-early*(sndr), *make-sender*(stopped_as_error, err, sndr)) except that sndr is only evaluated once[.](#2.sentence-4)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L4877)
+
+Let sndr and env be subexpressions
+such that Sndr is decltype((sndr)) andEnv is decltype((env))[.](#3.sentence-1)
+
+If [*sender-for*](exec.snd.concepts#concept:sender-for "33.9.3 Sender concepts [exec.snd.concepts]")<Sndr, stopped_as_error_t> is false,
+then the expression stopped_as_error.transform_sender(sndr, env) is ill-formed;
+otherwise, it is equivalent to:auto&& [_, err, child] = sndr;using E = decltype(auto(err));return let_stopped( std::forward_like<Sndr>(child), [err = std::forward_like<Sndr>(err)]() mutable noexcept(is_nothrow_move_constructible_v<E>) {return just_error(std::move(err)); });