Extended indexing operators (#1064)

* Extended indexing operators

This commit adds extended indexing operators to the parser.
For instance,

```
let (.%()) p (x,y) = p.( x ).( y )
;; p.%(0,0)

```
Extended indexing operators name starts with a leading
dot "." followed by an operator symbol, except "." or "<"
and a sequence of any operators and must be closes with a
couple of enclosing parentheses ( i.e. "()", "[]", "{}" )
and then an optional assignment operator "<-":

  * '.' dotsymbolchar symbolchar* '(' ')' ['<-']
  * '.' dotsymbolchar symbolchar* '[' ']' ['<-']
  * '.' dotsymbolchar symbolchar* '{' '}' ['<-']

Similarly, expressions of the form

* expr_1 '.' dotsymbolchar symbolchar* '(' expr_2 ')'
* expr_1 '.' dotsymbolchar symbolchar* '[' expr_2 ']'
* expr_1 '.' dotsymbolchar symbolchar* '{' expr_2 '}'

and

* expr_1 '.' dotsymbolchar symbolchar* '(' expr_2 ')' '<-' expr_3
* expr_1 '.' dotsymbolchar symbolchar* '[' expr_2 ']' '<-' expr_3
* expr_1 '.' dotsymbolchar symbolchar* '{' expr_2 '}' '<-' expr_3

are desugared to

* ('.' dotsymbolchar symbolchar* '(' ')' ) expr_1 expr_2
* ('.' dotsymbolchar symbolchar* '[' ']' ) expr_1 expr_2
* ('.' dotsymbolchar symbolchar* '{' '}' ) expr_1 expr_2

and

* ('.' dotsymbolchar symbolchar* '(' ')' '<-' ) expr_1 expr_2 expr_3
* ('.' dotsymbolchar symbolchar* '[' ']' ) expr_1 expr_2 expr_3
* ('.' dotsymbolchar symbolchar* '{' '}' '<-' ) expr_1 expr_2 expr_3

4 files changed, 51 insertions, 4 deletions

diff --git a/manual/manual/refman/expr.etex b/manual/manual/refman/expr.etex
index fdc3659b94..2824ae5cc0 100644
--- a/manual/manual/refman/expr.etex
+++ b/manual/manual/refman/expr.etex
@@ -118,8 +118,9 @@ See also the following language extensions:
 \hyperref[s:explicit-overriding-open]{overriding in open statements},
 \hyperref[s:bigarray-access]{syntax for Bigarray access},
 \hyperref[s:attributes]{attributes},
-\hyperref[s:extension-nodes]{extension nodes} and
-\hyperref[s:local-exceptions]{local exceptions}.
+\hyperref[s:extension-nodes]{extension nodes},
+\hyperref[s:local-exceptions]{local exceptions}
+\hyperref[s:index-operators]{extended indexing operators}.
 
 The table below shows the relative precedences and associativity of
 operators and non-closed constructions. The constructions with higher
diff --git a/manual/manual/refman/exten.etex b/manual/manual/refman/exten.etex
index 1f3b485b6b..a7cbe867b8 100644
--- a/manual/manual/refman/exten.etex
+++ b/manual/manual/refman/exten.etex
@@ -2351,3 +2351,45 @@ will be converted directly to
 type t =  T of string
 [@@ocaml.doc " Attaches to t "]
 \end{verbatim}
+
+\section{Extendend indexing operators \label{s:index-operators} }
+(Introduced in 4.06)
+
+\begin{syntax}
+
+dot-ext:
+   | ('!'||'$'||'%'||'&'||'*'||'+'||'-'||'/'||':'||'='||'>'||'?'||'@'||'^'||'|'||'~') { operator-char }
+;
+expr:
+          ...
+        | expr '.' dot-ext ( '(' expr ')' || '[' expr ']' || '{' expr '}' ) [ '<-' expr ]
+;
+operator-name:
+          ...
+        | '.' dot-ext ('()' || '[]' || '{}') ['<-']
+;
+\end{syntax}
+
+
+This extension provides syntactic sugar for getting and setting elements
+for user-defined indexed types. For instance, we can define python-like
+dictionaries with
+\begin{caml-example}
+module Dict = struct
+
+include Hashtbl
+let ( .%{} ) tabl index = find tabl index
+let ( .%{}<- ) tabl index value = add tabl index value
+end;;
+let dict =
+  let open Dict in
+  let dict = create 10 in
+  let () =
+    dict.%{"one"} <- 1;
+    dict.%{"two"} <- 2 in
+  dict
+;;
+let () =
+  let open Dict in
+  assert( dict.%{"one"} = 1 );;
+\end{caml-example}
diff --git a/manual/manual/refman/lex.etex b/manual/manual/refman/lex.etex
index 87634d3bdb..f1ac3ea1c9 100644
--- a/manual/manual/refman/lex.etex
+++ b/manual/manual/refman/lex.etex
@@ -218,8 +218,9 @@ operator-char:
         '/' || ':' || '<' || '=' || '>' || '?' || '@' ||
         '^' || '|' || '~'
 \end{syntax}
-See also the following language extension:
-\hyperref[s:ext-ops]{extension operators}.
+See also the following language extensions:
+\hyperref[s:ext-ops]{extension operators} and
+\hyperref[s:index-operators]{extended indexing operators}.
 
 Sequences of ``operator characters'', such as "<=>" or "!!",
 are read as a single token from the @infix-symbol@ or @prefix-symbol@
diff --git a/manual/manual/refman/names.etex b/manual/manual/refman/names.etex
index bad503395b..4f85eed44a 100644
--- a/manual/manual/refman/names.etex
+++ b/manual/manual/refman/names.etex
@@ -73,6 +73,9 @@ inst-var-name:
 method-name:
     lowercase-ident
 \end{syntax}
+See also the following language extension:
+\hyperref[s:index-operators]{extended indexing operators}.
+
 As shown above, prefix and infix symbols as well as some keywords can
 be used as value names, provided they are written between parentheses.
 The capitalization rules  are summarized in the table below.