JEP-14 Compact syntax for multi-select-hash

proposals/draft/jep-014-es6-style-compact-hash.md

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+# Compact syntax for multi-select-hash
+
+|||
+|---|---
+| **JEP**    | 14
+| **Author** | Dan Vanderkam, Maxime Labelle
+| **Status** | draft
+| **Created**| 26-Feb-2022
+
+## Abstract
+
+This JEP proposes a grammar modification to support
+[ES6](https://www.benmvp.com/blog/learning-es6-enhanced-object-literals/)-style
+compact `multi-select-hash` constructs.
+
+## Motivation
+
+Consider the following JSON document:
+
+```
+{
+  "values": [
+    {"id": 1, "first": "Bill", "last": "Gates"},
+    {"id": 2, "first": "Larry", "last": "Page"}
+  ]
+}
+```
+
+Let’s say we wanted to return a hash containing `id`s and `first` names.
+This is currently possible using the following syntax:
+
+```
+values[*].{id:id, first:first}
+```
+
+Since `{x:x, y:y}` is such a common pattern, ES6 introduced compact object literal notation to simplify this. In ES6, `{x,y}` is equivalent to `{x:x, y:y}`.
+
+This JEP supports this syntax to make JMESPath usage slightly less verbose.
+
+## Specification
+
+What is currently the `multi-select-hash` production will be renamed
+to `multi-select-hash-keyval`:
+
+```
+multi-select-hash_keval = "{" ( keyval-expr *( "," keyval-expr ) ) "}"
+```
+
+The `multi-select-hash` production will be modified slightly to accomodate
+the syntax changes:
+
+```
+multi-select-hash	= multi-select-hash-key
+multi-select-hash	=/ multi-select-hash-keyval
+```
+
+The new `multi-select-hash-key` production is defined like so:
+
+```
+multi-select-hash-key = "{" ( identifier *( "," identifier ) ) "}" 
+```
+
+Here is the full update to the grammar:
+
+```
+multi-select-hash        = multi-select-hash-key
+multi-select-hash        =/ multi-select-hash-keyval
+
+multi-select-hash-key    = "{" ( identifier *( "," identifier ) ) "}" 
+multi-select-hash-keyval = "{" ( keyval-expr *( "," keyval-expr ) ) "}"
+```
+
+### Motivating Example
+
+With these changes defined, the expression in the “Motivation” section can be
+be written as:
+
+```
+values[*].{id, first}
+```
+
+Which evaluates to `[{"id": 1, "first": "Bill"}, {"id": 2, "first": "Larry"}]`.
+
+## Rationale
+
+This JEP is inspired by [an idea](https://github.com/jmespath/jmespath.site/issues/43)
+from Dan Vanderkam.