Visitor that converts AST nodes back to string expressions.

This visitor implements the inverse of parsing - it takes an Abstract Syntax Tree and generates a readable string representation. This is useful for debugging, documentation, and round-trip testing.

A node's trailing slot is ignored: rendering a parsed AST and rendering the same tree with nil in every slot produce identical strings. A caller hand-building an AST supplies nil there - the slot is part of the node shape, not an add-on.

Examples

iex> ast = {:literal, 42, nil}
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"42"

iex> ast = {:identifier, "score", nil}
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"score"

iex> ast = {:comparison, :gt, {:identifier, "score", nil}, {:literal, 85, nil}, nil}
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"score > 85"

iex> {:ok, ast} = Predicator.parse(~s(name == "John"))
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
~s(name == "John")

iex> ast = {:logical_and, {:literal, true, nil}, {:literal, false, nil}, nil}
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"true AND false"

iex> ast = {:logical_not, {:literal, true, nil}, nil}
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"NOT true"

iex> ast = {:function_call, "len", [{:identifier, "name", nil}], nil}
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"len(name)"

iex> ast = {:cast, {:identifier, "score", nil}, "integer", nil}
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"score::integer"

iex> ast = {:object, [], nil}
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"{}"

iex> {:ok, ast} = Predicator.parse(~s({name: "John"}))
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
~s({name: "John"})

iex> {:ok, ast} = Predicator.parse(~s({"first name": "John"}))
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
~s({"first name": "John"})

iex> {:ok, ast} = Predicator.parse_program("if a { x = 1 } else if b { x = 2 }")
iex> Predicator.Visitors.StringVisitor.visit(ast, [])
"if a { x = 1 } else if b { x = 2 }"