Chapter 8  Language extensions

This chapter describes language extensions and convenience features that are implemented in OCaml, but not described in the OCaml reference manual.

20  Extended indexing operators

(Introduced in 4.06)

dot-ext::=  
 ∣ (!∣ $∣ %∣ &∣ *∣ +∣ -∣ /∣ :∣ =∣ >∣ ?∣ @∣ ^∣ |∣ ~) { operator-char }  
 
expr::= ...  
 ∣ expr .  [module-path .]  dot-ext  ( ( expr ) ∣  [ expr ] ∣  { expr } )  [ <- expr ]  
 
operator-name::= ...  
 ∣ . dot-ext  (() ∣  [] ∣  {}) [<-]  
 

This extension provides syntactic sugar for getting and setting elements for user-defined indexed types. For instance, we can define python-like dictionaries with 

 module Dict = struct
 include Hashtbl
 let ( .%{} ) tabl index = find tabl index
 let ( .%{}<- ) tabl index value = add tabl index value
 end
 let dict =
   let dict = Dict.create 10 in
   let () =
     dict.Dict.%{"one"} <- 1;
     let open Dict in
     dict.%{"two"} <- 2 in
   dict



 dict.Dict.%{"one"};;

- : int = 1

 let open Dict in dict.%{"two"};;

- : int = 2
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