feat(function-call): add alternative lambda syntax

docs/index.md

@@ -62,7 +62,6 @@ returned.
 
 In any other case, a list of each requested element is returned.
 
-
 ### Functions
 
 #### `join`
@@ -90,19 +89,19 @@ separator.
 Input:
 
 ```
-["Hello", "World!"] | map \{"word": $}
+["Hello", "World!"] | map $ => {"word": $}
 ```
 
 Output:
 
 ```json
-[
-  { "word": "Hello"},
-  { "word": "World!"},
-]
+[{"word": "Hello"}, {"word": "World!"}]
 ```
 
+Alternatively, you can also use this syntax: `["Hello", "World!"] | map \ {"word": $}`
+
 ### Chaining filters
+
 You can combine two filters by using the pipe syntax, e. q. `.foo | .bar`
 
 The first filter (`.foo`) will receive the input and transform it; the second

src/parsers/__tests__/functionCallLambda.test.js

@@ -4,6 +4,21 @@ describe('functionCallLambda parser', () => {
   it('parses map \\"foo"', () => {
     expect(parser.parse('map \\"foo"').status).toBe(true)
   })
+  it('parses map \\ "foo"', () => {
+    expect(parser.parse('map \\ "foo"').status).toBe(true)
+  })
+
+  it('parses map $ => "foo"', () => {
+    expect(parser.parse('map $ => "foo"').status).toBe(true)
+  })
+
+  it('parses map $ =>"foo"', () => {
+    expect(parser.parse('map $ =>"foo"').status).toBe(true)
+  })
+
+  it('parses map $=>"foo"', () => {
+    expect(parser.parse('map $=>"foo"').status).toBe(true)
+  })
 
   it('returns correct value', () => {
     expect(parser.parse('map \\["a", "b"]').value).toEqual({

src/parsers/functionCallLambda.js

@@ -14,7 +14,7 @@ const FunctionCallLambdaParser = Parsimmon.lazy((): mixed => {
   return Parsimmon.seq(
     IdentifierParser,
     Parsimmon.optWhitespace,
-    Parsimmon.string('\\'),
+    Parsimmon.alt(Parsimmon.regexp(/\$\s*=>\s*/), Parsimmon.string('\\')),
     Parsimmon.optWhitespace,
     ProgramParser
   ).map(