Mercurial > urweb
changeset 1548:76dab73304a5
Document monadic shorthands
author | Adam Chlipala <adam@chlipala.net> |
---|---|
date | Wed, 24 Aug 2011 08:18:09 -0400 (2011-08-24) |
parents | 553a5cc3a4b5 |
children | 355a928871ff |
files | doc/manual.tex |
diffstat | 1 files changed, 2 insertions(+), 0 deletions(-) [+] |
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--- a/doc/manual.tex Sun Aug 21 13:41:57 2011 -0400 +++ b/doc/manual.tex Wed Aug 24 08:18:09 2011 -0400 @@ -1389,6 +1389,8 @@ \hspace{.1in} \to \mt{monad} \; \mt{m} \end{array}$$ +The Ur/Web compiler provides syntactic sugar for monads, similar to Haskell's \cd{do} notation. An expression $x \leftarrow e_1; e_2$ is desugarded to $\mt{bind} \; e_1 \; (\lambda x \Rightarrow e_2)$, and an expression $e_1; e_2$ is desugared to $\mt{bind} \; e_1 \; (\lambda () \Rightarrow e_2)$. + \subsection{Transactions} Ur is a pure language; we use Haskell's trick to support controlled side effects. The standard library defines a monad $\mt{transaction}$, meant to stand for actions that may be undone cleanly. By design, no other kinds of actions are supported.