print-ast.ts

// Prints the AST of an expression.

function indent(text: string) {
    return text.replace(/\n/g, "\n  ")
}

function printArray(value: readonly unknown[]) {
    return " " + indent(printAST(value))
}

function printASTKey([key, value]: [string, unknown]) {
    if (value === void 0) {
        return ""
    }

    return (
        "\n  "
        + key
        + ":"
        + (Array.isArray(value) ? printArray(value)
        : typeof value == "object" && value ?
            "\n    " + indent(indent(printAST(value)))
        :   " " + JSON.stringify(value))
    )
}

export function printAST(node: unknown): string {
    if (typeof node != "object" || node == null) {
        return JSON.stringify(node)
    }

    return `${
        "type" in node ?
            String(node.type)[0]?.toUpperCase() + String(node.type).slice(1)
        :   node.constructor.name
    }${Object.entries<unknown>(node as {})
        .filter(([key]) => key != "type")
        .map(printASTKey)
        .join("")}`
}