simple dsl language in peg js

1/**********
2 Starting rule, our entry point to the parser.
3 The first part of the PEG extracts the entity name as a string, 
4 and makes the "entity" accessible in the JS below, allowing us to the AST and return it. 
5 It matches certain expected keywords, eg. "has", but does nothing with them. 
6 Finally it extracts the values, which have already been turned into a Values AST. 
7 You'll see the "_" rule used here, this means "accept/skip whitespace", it's defined below.
8**********/
9Command = entity:Var "." command:Var _ "has" _ "nothing"* _ values:Values* _
10  {
11    // Handle case that there are no values
12    values = values.length === 0 ? [] : values[0];
13
14    // Return the matched results with this object structure
15    return {
16      entity: entity,
17      command: command,
18      values: values
19    }
20  }
21
22/**********
23 Matches a collection of inputs, 0 to many, that are wrapped in parentheses
24**********/
25Values = "{" _ values:(CompositeValue/Value)* _ "}"
26  {
27    return values;
28  }
29
30/**********
31 Value and CompositeValues always have the same initial shape, so I extracted 
32 this into a partial result that is extended by both Value and Composite
33**********/
34ValuePartial = _ "a" [n]? _ cls:Var _ name:Var _
35  {
36    return {
37      class: cls,
38      param: name
39    }
40  }
41
42Value = value:ValuePartial alias:(Alias)? _
43  {
44    value.requestParam = (alias) ? alias: value.param;
45    value.type = 'value';
46    return value;
47  }
48
49/**********
50 Extract the alias value, ignore the "from" string
51**********/   
52Alias = _ "from" _ alias:Var 
53  {
54    return alias;
55  }
56
57CompositeValue = value:ValuePartial "from" _ values:Values
58  {
59    value.type = 'composite';
60    value.values = values;
61    return value;
62  }
63
64Var = name:[A-Za-z0-9_]*
65  {
66    return name.join("");
67  }
68
69/**********
70 Match any sequence of "whitespace" characters
71**********/   
72_ = [ \t\n\r]*
73