Mercurial > urweb
comparison doc/manual.tex @ 1548:76dab73304a5
Document monadic shorthands
| author | Adam Chlipala <adam@chlipala.net> |
|---|---|
| date | Wed, 24 Aug 2011 08:18:09 -0400 |
| parents | a99b743a3087 |
| children | 5175bed443f9 |
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| 1547:553a5cc3a4b5 | 1548:76dab73304a5 |
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| 1387 \hspace{.1in} \to \{\mt{Return} : \mt{t} ::: \mt{Type} \to \mt{t} \to \mt{m} \; \mt{t}, \\ | 1387 \hspace{.1in} \to \{\mt{Return} : \mt{t} ::: \mt{Type} \to \mt{t} \to \mt{m} \; \mt{t}, \\ |
| 1388 \hspace{.3in} \mt{Bind} : \mt{t1} ::: \mt{Type} \to \mt{t2} ::: \mt{Type} \to \mt{m} \; \mt{t1} \to (\mt{t1} \to \mt{m} \; \mt{t2}) \to \mt{m} \; \mt{t2}\} \\ | 1388 \hspace{.3in} \mt{Bind} : \mt{t1} ::: \mt{Type} \to \mt{t2} ::: \mt{Type} \to \mt{m} \; \mt{t1} \to (\mt{t1} \to \mt{m} \; \mt{t2}) \to \mt{m} \; \mt{t2}\} \\ |
| 1389 \hspace{.1in} \to \mt{monad} \; \mt{m} | 1389 \hspace{.1in} \to \mt{monad} \; \mt{m} |
| 1390 \end{array}$$ | 1390 \end{array}$$ |
| 1391 | 1391 |
| 1392 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 $\mt{bind} \; e_1 \; (\lambda () \Rightarrow e_2)$. | |
| 1393 | |
| 1392 \subsection{Transactions} | 1394 \subsection{Transactions} |
| 1393 | 1395 |
| 1394 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. | 1396 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. |
| 1395 $$\begin{array}{l} | 1397 $$\begin{array}{l} |
| 1396 \mt{con} \; \mt{transaction} :: \mt{Type} \to \mt{Type} \\ | 1398 \mt{con} \; \mt{transaction} :: \mt{Type} \to \mt{Type} \\ |