Learning OCaml: PPX for Mere Mortals
a day ago
- #CompileTime
- #OCaml
- #Metaprogramming
- PPX (PreProcessor eXtensions) generates code at compile time in OCaml by transforming the Abstract Syntax Tree (AST), addressing the lack of runtime reflection.
- Common PPX libraries include ppx_deriving for pretty-printing, equality, and ordering; ppx_deriving_yojson for JSON serialization; and ppx_sexp_conv for S-expression serialization.
- PPX syntax includes extension nodes like [%here] and attributes like [@@deriving show], with the latter being widely used for type declarations.
- Using PPX in projects involves adding libraries to the preprocess stanza in dune files, and debugging can be done with commands like dune describe pp.
- PPX evolution includes consolidation around ppxlib, with built-in binding operators in OCaml 4.08 reducing reliance on some PPX libraries.