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The language

The lexer and parser packages cover the Puppet 8 grammar and produce a Puppet::Pops-style AST (the ast package). The ast.Sexpr renderer prints a compact s-expression of any node, which is how the parser is asserted in tests.

Literals & interpolation

  • Integers (decimal, 0x hex, 0 octal), floats, booleans, undef, default.
  • Single-quoted strings (only \' and \\ escapes) and double-quoted strings with ${…} / $var interpolation and \n \t \r \s \u{…} escapes.
  • Arrays […] and hashes { k => v }.
  • Regular expressions /…/.
$greeting = "hello ${upcase('world')} — ${1 + 2}"

Inside ${…}, a lower-case leading word is an implicit variable (${os} ≡ $os); an upper-case word is a type or resource reference (${File['x']}); a word immediately followed by ( is a function call.

Heredocs

@(TAG) (no interpolation) or @("TAG") (interpolation on), with an optional :syntax tag, a | indent margin and a - trailing-newline chomp:

$config = @("EOT")
  server ${host}
  | EOT

Data-type expressions

Data types such as Integer[1,10], Optional[String], Enum['a','b'] and Array[Integer] are parsed as AST and evaluated through go-pcore — they are never reimplemented here.

Operators

The full precedence ladder: unary ! - *, in, =~/!~, * / %, + -, <<, == !=, < > <= >=, and, or, assignment =, and the relationship operators -> ~> <- <~.

Whitespace-sensitive [

Following Puppet, a [ with preceding whitespace after a non-reference starts a new array/statement rather than indexing; $x[0] indexes, but $x [0] is two expressions.

Control flow

if/elsif/else, unless, case (with value, Regexp and Type matching) and selectors $x ? { … }.

Resources & definitions

Resource declarations, defaults Type { }, overrides Type[t] { }, collectors <| |> / <<| |>>, virtual @ and exported @@ forms; class (with inherits), define, node, and function (with >> ReturnType) definitions; function calls with lambdas |params| { }; and relationship chaining.