@formscript/ast

The abstract syntax tree of §4 of the specification: the node types every production in the grammar can produce.

This package depends on nothing. The node definitions are the contract between the lexer, the parser, the scope builder, the analyser and the engine, so they are kept free of even a dependency on the error catalogue.

Nodes

Every node is a discriminated union member with a kind and a span:

import type { Expression, Statement } from '@formscript/ast';

function describe(node: Expression): string {
  switch (node.kind) {
    case 'identifier': return node.name;
    case 'literal': return node.raw;
    default: return node.kind;
  }
}

SourceSpan is a half-open range with 1-based line and column, plus the byte offset, so a diagnostic can point at the exact source text that caused it.

Walking

import { allExpressions, allStatements, childExpressions } from '@formscript/ast';

for (const expression of allExpressions(document)) {
  // every expression in the document, each node once
}

for (const child of childExpressions(expression)) {
  // the direct children of one expression
}

allExpressions returns each node once, in source order, which is what the diagnostic order of §9.9 requires.

Public API

89 exported symbols.