ANNOUNCEMENT: PowerPatch for Set Constructor Syntax Published

["John Hind" <john.hind@...>]

As discussed in "Set Constructor Syntax (Was: Help with Lexer/Parser
Internals Please!)" I have published a PowerPatch here:

http://lua-users.org/wiki/LuaPowerPatches

The patch updates the manual as well as the source code. Here is the
relevant manual update:

3.4.9 - Table Constructors

Table constructors are expressions that create tables. Every time a
constructor is evaluated, a new table is created. A constructor can be 
used to create an empty table or to create a table and initialize some of
its fields. The general syntax for constructors is

	tableconstructor ::= '{' [fieldlist] '}'
	fieldlist ::= field {fieldsep field} [fieldsep]
	field ::= '[' exp ']' '=' exp | '.' Name '=' exp | '[' exp ']' | '.'
Name | 
		Name '=' exp | exp
	fieldsep ::= ',' | ';'

[JH-LUA-SETINIT]: The two '.Name' and the '[exp]' field syntax options are
added by the powerpatch.

Each field of the form '[exp1] = exp2' adds to the new table an entry with
key 'exp1' and value 'exp2'. A field of the form 'name = exp' or 
'.name = exp' is equivalent to '["name"] = exp'. Fields of the form 'exp'
are equivalent to '[i] = exp', where i are consecutive integers starting 
with 1. Fields in the other formats do not affect this counting. For
example,

(example is unchanged)

A field of the form '[exp]' is equivalent to '[exp] = true' and a field of
the form '.name' is equivalent to '["name"] = true'.

(end of manual extract)

Although this was motivated by the desire to provide a syntax shortcut for
set-like tables similar to the existing one for list-like tables,
I also think the period prefix for name keys (optional if the value is also
specified) is an improvement more generally. By echoing the
table access syntax, it makes clearer what is going on and preserves the
"user illusion" that this is a name scope-limited to the table
rather than a string key.

The patch introduces no incompatibilities and adds only 16 lines of code.

- John Hind


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