buffer-builder

Data.BufferBuilder is an efficient library for incrementally building up ByteStrings, one chunk at a time. Early benchmarks show it is over twice as fast as ByteString Builder, primarily because BufferBuilder is built upon an ST-style restricted monad and mutable state instead of ByteString Builder's monoidal AST. Internally, BufferBuilder is backed by a few C functions. Examination of GHC's output shows nearly optimal code generation with no intermediate thunks -- and thus, continuation passing and its associated indirect jumps and stack traffic only occur when BufferBuilder is asked to append a non-strict ByteString. I benchmarked four approaches with a URL encoding benchmark: State monad, concatenating ByteStrings: 6.98 us State monad, ByteString Builder: 2.48 us Crazy explicit RealWorld baton passing with unboxed state: 28.94 us (GHC generated really awful code for this, but see the revision history for the technique) C + FFI + ReaderT: 1.11 us Using BufferBuilder is very simple: This package also provides Data.BufferBuilder.Utf8 for generating UTF-8 buffers and Data.BufferBuilder.Json for encoding data structures into JSON.