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Deprecated, use ppx_compare instead
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Pa_compare is a camlp4 syntax extension that derives comparison functions from type representations. The scaffolded functions are usually much faster than ocaml's [Pervasives.compare] (cf. the programs in benchmark/). Scaffolding functions also gives you more flexibilty by allowing you to override them for a specific type and more safety by making sure that you only compare comparable values. We use the type_conv framework so: [ type s = v * w with compare ] will generate and [compare_s : s -> s -> int ] function that relies on [compare_v : v -> v -> int] and [compare_w : w -> w -> int]. ______________________________________________________________________________ | . | | /!\ Compare is not DWIM (do what I mean) : it will scaffold a fast | | ^^^ well behaved comparison (reflexive, transitive, symmetric...) function | | however it does not try to follow any "natural ordering". For instance | | arrays of characters are not sorted lexicographically. | |______________________________________________________________________________| Base types (options,int,array,lists,char,floats...) have the same comparison order than Pervasives.compare (providing their type parameters also do for the polymorphic ones). Records fields are compared in the order they are defined (left to right); tuples fields are compared left to right. When we compare two branches of a sum whichever ones comes first in the definition is considered lowest. Variants use a fairly odd ordering (the same as the ocaml runtime)... special features: Calling [compare] for type [t]s ================================ In compliance (or conformance) with Janestreet's coding standard we assume that type named [t] are the main types in a module and [ type t = S.t * T.t with compare ] will call the functions [S.compare] and [T.compare] instead of calling [S.compare_t] and [T.compare_t]. This will also generate a [compare : t -> t -> int] function the [compare_t] function is also generated for consistency's sake. Signature ========= [type t with compare] in a module signature will add the [ compare : t -> t -> int ] function in the signature (please note that the functions [compare_t] is not exported...). Quotation ========== Sometimes you just want to compare values and not to create new types for them. You can call the comparison function for a specific input?argument?using quotations: [ let gt x y = <:compare< float * int * [`A | `B | `C] >> x y ] Tasking compare for a quick spin ================================ The [preprocess.sh] script will show you the result of applying the syntax extension to a file. If you have your type definition in a file [f.ml] you can look at the generated comparison functions by calling [preprocess.sh f.ml]