0005 - Literal syntax for collections

pheps-0005.md

@@ -0,0 +1,67 @@
+```
+PhEP {
+	#id: 0005,
+	#type: #image,
+	#title: 'Literal syntax for collections',
+	#status: 'proposal',
+	#authors: [ 'Stéphane Ducasse' ],
+	#created: '2023-09-17'
+}
+```
+
+# Abstract 
+
+A proposal to be able to write literal collections in the same way we have DynamicArray.
+The proposal is based on the idea of Dave Mason to support `{:Set 1 . 2 . 1}` to get a set with 2 elements. This approach works for any collection (assuming that they implement `withAll:`). Also some other objects could benefit from this new notation, e.g. `Point` or `Rectangle`. For this reason, it will be best to define a new selector that will be used by the Brace Litteral syntax: `withAllForBrace:`.
+
+# Changelog
+
+- 2023-09-17: initial document
+
+# Motivation
+
+The following illustrates the point: 
+
+```
+(Set new add: 1 ; add: (Set new add: 2; add: 2; yourself);  add: 1 ;yourself)
+```
+
+When scripting we would like to be able to write:
+
+```
+{:Set 1 . {:Set 2 . 2} . 1}
+```
+
+Similarly people could write
+
+```
+{:Dictionary #a -> 33 . #b -> 44 }
+```
+
+# Discussion
+
+This design is nice since there is no look-ahead. It is familiar in the sense that it uses : to denote a kind of argument (here it is the class of the collection).
+
+In addition, we do not use another special character or character sequence such as `{{` or `#{` or whatever.
+
+## Possible questions for another iteration
+
+The compiler could check that the class defines the method `withAllForBrace:`.
+
+# Implementation 
+
+It is done and minimal: on extra tree node. We should just move the methods of the `RBParserLiteralCollection` to its superclass. We should check the syntax hilighter. The pretty printing has been fixed.
+
+```
+testNestedLiteralSet
+
+	| compiler |
+	compiler := OpalCompiler new.
+	compiler compilationContext parserClass: RBParserLiteralCollection. 
+	self assert: (compiler evaluate: 
+		'{ :Set 1 . {  :Set 2 . 2 } . 1}' )
+
+		equals:  (Set new add: 1 ; add: (Set new add: 2; add: 2; yourself);  add: 1 ;yourself).
+```
+
+See Pull Request https://github.com/pharo-project/pharo/pull/14845