Unparser

Unparser

The unparser is the inverse of the builder: ASDL nodes become source text with correct operator parenthesization and Pine idioms (=>, :=, var/varip, export, method vs function).

Abstract

src/pynescript/ast/unparser.py implements NodeUnparser(NodeVisitor) and a Precedence enum. helper.unparse(node) calls unparse_node, which reuses a thread-local NodeUnparser (warm type-visitor cache; visit still resets the buffer each call). Output is semantically faithful, not a pretty-printer of original trivia: whitespace is normalized; comments that never became annotations are not reconstructed; annotation strings that were attached are re-emitted.

Round-trip tests (parse → unparse → parse) are the primary oracle for grammar/builder/unparser coherence.

Conceptual model

Rendering…

Parenthesization: higher Precedence values bind tighter (TEST loosest, ATOM tightest). A node is wrapped in () when the precedence stored on it (the parent context) is strictly greater than the node’s own operator level. Equal levels do not wrap (left-associative chains).

Interface surface

from pynescript.ast.helper import parse, unparse

src = """
//@version=6
f(x) => x * 2
plot(f(close))
"""
print(unparse(parse(src)))

Precedence (low → high binding)

Matches IntEnum order in unparser.py:

Precedence.next() steps one level tighter for right-hand associativity control. Bitwise tokens are emitted from visit_BinOp / visit_UnaryOp maps (BitAnd/BitOr/BitXor/LShift/RShift/Invert), not standalone visit_BitAnd methods.

Buffer helpers (internal but useful when subclassing)

Node coverage (high level)

Internals

Path

• src/pynescript/ast/unparser.py — Precedence, NodeUnparser, unparse_node
• Entry: helper.unparse → unparse_node → thread-local NodeUnparser.visit

Visit vs traverse

visit resets _source, _precedences, and _indent, then calls traverse. traverse accepts lists (statement bodies) or single nodes, then dispatches via _type_visitor_cache (type-object keys, not class-name strings). This split lets statement lists and expression trees share code without double-buffering.

visit_FunctionDef emits returns (when set) as a leading type spec: export method int name(args) => ….

If / else if chains

visit_If detects orelse == [Expr(If(...))] and emits else if rather than nested else + if blocks — matching idiomatic Pine.

visit_Once emits once plus an optional test and an indented body.

Type body ordering

visit_TypeDef partitions body into field statements vs FunctionDef with method set, emitting fields first then methods.

Constants

String constants use JSON-style quoting helpers where needed; colors and numbers re-serialize from their Python values. Exact original quote style (single vs double) is not guaranteed.

Invariants

1. Precedence tables must stay aligned with the parser’s expression layers (including bitwise | ^ & << >> between and and comparisons). A mismatch causes either redundant parens (benign) or wrong binding after re-parse (severe).
2. Annotations are part of the round-trip surface when attached to Script/FunctionDef/TypeDef/Assign.
3. Unparser does not type-check. Ill-typed but well-shaped trees still print.
4. Indent unit is four spaces (" " * self._indent).

Worked examples

Precedence

from pynescript.ast.helper import parse, unparse

# Builder produces BinOp(Add, left=1, right=BinOp(Mult, 2, 3)) or inverse depending on parse
print(unparse(parse("1 + 2 * 3", mode="eval")))
# Expect something that re-parses to the same value: e.g. "1 + 2 * 3"

Function forms

# Single-expression body → f(x) => expr
# Multi-statement body → f(x) =>\n    stmt\n    stmt
# With return type → int f(x) => expr
# Method → method int f(self) => expr

Reassignment vs declaration

// Assign with mode → var float x = 1.0
// ReAssign → x := 2.0
// AugAssign → x += 1

Failure modes

See also

• Helper API
• Builder
• ASDL schema
• Visitor / transformer