When comparing Postgrest vs Snap, the Slant community recommends Snap for most people. In the question“What are the best Haskell web frameworks for building RESTful web services?” Snap is ranked 7th while Postgrest is ranked 8th. The most important reason people chose Snap is:
Snap provides "snaplets". These are self-contained modules of code that provide additional functionality without muddling the core library. Having these resources saves time when developing code.
Specs
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Pros
Pro Fast
JSON is handled by PostgreSQL which speed is hard to beat in your own applications.
Response times as high as 2000 requests/sec on Heroku free tier.
Pro Easy to use
Pro Linux, Windows, FreeBSD, OS-X
Linux, Windows, FreeBSD, OS-X versions available.
Pro Provides modules for changeable functionality
Snap provides "snaplets". These are self-contained modules of code that provide additional functionality without muddling the core library. Having these resources saves time when developing code.
Cons
Con Outdated documentation
The comprehensive Snap documentation is currently outdated (last activity appears to have been 2013), though Snap itself is under active development. Note that this primarily affects tutorials and guides; the API documentation is generated automatically and remains current.