Minimalistic library and syntax extension for type-safe, convenient execution of sql statements. currently compatible with sqlite3.

sqlexpr features:
* automated prepared statement caching, param binding, data extraction, error
checking (including automatic stmt reset to avoid busy/locked errors in
subsequent queries), stmt finalization on db close, etc.
* hofs like iter, fold, transaction
* support for different concurrency models: everything is functorized over a
thread monad, so you can for instance do concurrent folds/iters with lwt
* support for sql stmt syntax checks and some extra semantic checking (column
names, etc)