Mercurial > urweb
changeset 2042:336070df8aec
Manual: Heuristic compilation warning
| author | Adam Chlipala <adam@chlipala.net> |
|---|---|
| date | Sat, 26 Jul 2014 09:39:45 -0400 |
| parents | ec7a1fa5e88f |
| children | e762c96fffb7 |
| files | doc/manual.tex |
| diffstat | 1 files changed, 7 insertions(+), 3 deletions(-) [+] |
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--- a/doc/manual.tex Sat Jul 26 09:26:11 2014 -0400 +++ b/doc/manual.tex Sat Jul 26 09:39:45 2014 -0400 @@ -377,6 +377,10 @@ \item \cd{URWEB\_PQ\_CON}: when using PostgreSQL, overrides the compiled-in connection string \end{itemize} +\subsection{A Word of Warning on Heuristic Compilation} + +For server-side code, Ur/Web follows an unusual compilation model, where not all type-correct programs can be compiled successfully, especially when using functions as data not known until runtime. See Section \ref{phases} for more detail. + \section{Ur Syntax} @@ -2555,9 +2559,9 @@ When no \texttt{jsFunc} directive is present, the function is assumed to map to a JavaScript function of the same name, if used in a client-side context. -\section{Compiler Phases} - -The Ur/Web compiler is unconventional in that it relies on a kind of \emph{heuristic compilation}. Not all valid programs will compile successfully. Informally, programs fail to compile when they are ``too higher order.'' Compiler phases do their best to eliminate different kinds of higher order-ness, but some programs just won't compile. This is a trade-off for producing very efficient executables. Compiled Ur/Web programs use native C representations and require no garbage collection. +\section{\label{phases}Compiler Phases} + +The Ur/Web compiler is unconventional in that it relies on a kind of \emph{heuristic compilation}. Not all valid programs will compile successfully. Informally, programs fail to compile when they are ``too higher order.'' Compiler phases do their best to eliminate different kinds of higher order-ness, but some programs just won't compile. This is a trade-off for producing very efficient executables. Compiled Ur/Web programs use native C representations and require no garbage collection. Also, this warning only applies to server-side code, as client-side code runs in a normal JavaScript environment with garbage collection. In this section, we step through the main phases of compilation, noting what consequences each phase has for effective programming.