Update to a more jq-like syntax and behavior

Signed-off-by: Ashley Jeffs <[email protected]>

rfcs/2020-07-21-2744-vicscript.md

@@ -23,16 +23,16 @@ Joining events are within scope, but aggregation of those events is not. For exa
 
 ## Guide Level Proposal
 
-The `vicscript` transform allows you to construct a new event by defining a sequence of mapping statements from a source event. Each mapping statement describes a read-only query operation on the right hand side, and on the left hand side a destination for the query result to be mapped within the resulting event:
+The `vicscript` transform allows you to mutate events by defining a sequence of mapping statements. Each mapping statement describes a read-only query operation on the right hand side, and on the left hand side a destination for the query result to be mapped within the resulting event:
 
 ```toml
 [transforms.mapper]
   inputs = [ "foo" ]
   type = "vicscript"
   mapping = """
-foo = "hello"
-bar = bar + 10
-baz_is_large = baz > 10
+.foo = "hello"
+.bar = .bar + 10
+.baz_is_large = .baz > 10
 """
 ```
 
@@ -41,77 +41,45 @@ baz_is_large = baz > 10
 The most common query type is a dot separated path, describing how to reach a target field within the input event:
 
 ```coffee
-foo = bar.baz.0.buz
+.foo = .bar.baz.0.buz
 ```
 
 Path sections that include whitespace or other special characters (including `.`) can be quoted:
 
 ```coffee
-foo = bar."baz.buz".bev
+.foo = .bar."baz.buz".bev
 
 # Use slash escapes within quotes
-bar = buz."fub\"\\fob".fab
+.bar = .buz."fub\"\\fob".fab
 ```
 
 And supports coalescing fields within a path with a pipe operator `|`, where if the first value is null or missing then the next value is selected, and so on:
 
 ```coffee
-foo = bar.(baz | buz).bev
-```
-
-You can assign a value to the root of your event by writing to the `root` keyword:
-
-```coffee
-root = nested.object
+.foo = .bar.(baz | buz).bev
 ```
 
 Vicscript supports float, int, boolean, string, null, array and object literals:
 
 ```coffee
-first = 7
-second = false
-third = "string"
-fourth = null
-```
-
-As well as a timestamp type:
-
-```coffee
-# NOTE: The full API for the timestamp type is out of the scope of this RFC. The
-# following example is for demonstrative purposes.
-
-created_at = now().unix()
-# Sets `created_at` to an integer representing the current unix timestamp
-# (in seconds).
+.first = 7
+.second = false
+.third = "string"
+.fourth = null
 ```
 
 Boolean operators and arithmetic galore:
 
 ```coffee
-is_big = number > 100
-multiplied = number * 7
+.is_big = .number > 100
+.multiplied = .number * 7
 ```
 
 Perform assignments conditionally with an `if` statement:
 
 ```coffee
-id = id
-sorted_foo = if foo.type() == "array" { foo.sort() }
-```
-
-```text
-In:  {"id":"first","foo":"not an array"}
-Out: {"id":"first"}'
-
-In:  {"id":"second","foo":["c","a","d","b"]}
-Out: {"id":"second","sorted_foo":["a","b","c","d"]}
-```
-
-The resulting event will only contain fields that are explicitly mapped, in order to begin your map with a full copy of the input event structure you can start by assigning `this` to `root`:
-
-```coffee
-root = this
-sorted_foo = if foo.type() == "array" { foo.sort() }
+.id = .id
+.sorted_foo = if .foo.type() == "array" { .foo.sort() }
 ```
 
 ```text
@@ -122,22 +90,12 @@ In:  {"id":"second","foo":["c","a","d","b"]}
 Out: {"id":"second","foo":["c","a","d","b"],"sorted_foo":["a","b","c","d"]}
 ```
 
-Use a wealth of methods on values in order to perform common mutations on them, since the underlying value is immutable these operations are safe to use in any combination:
+Remove fields by assigning them the `delete` keyword:
 
-```coffee
-sorted = foo.sort()
-uppercase = bar.uppercase()
-```
-
-```
-In:  {"foo":["c","a","d","b"],"bar":"hello world"}
-Out: {"sorted":["a","b","c","d"],"uppercase":"HELLO WORLD"}
+```text
+.foo = delete
 ```
 
-## Examples
-
-I've written an implementation of [an embedded CSV parser](2020-07-21-2744-vicscript/example1.coffee) using the above proposal in order to demonstrate what it looks like. This example is currently runnable with Benthos, and I've used the `.coffee` suffix because the syntax highlighting for CoffeeScript basically gives us everything we need already.
-
 ## Prior Art
 
 ### JQ