/**
 * S-FEEL 子集的抽象语法树(编码规范 §8.3)。
 * AST 是可 diff、可静态检查的中间形态 —— 前端画布的即时校验与后端裁决同源。
 */

export type Node =
  | { readonly kind: 'literal'; readonly value: number | string | boolean | null }
  | { readonly kind: 'path'; readonly segments: readonly string[] }
  | { readonly kind: 'unary'; readonly op: '-' | 'not'; readonly operand: Node }
  | {
      readonly kind: 'binary';
      readonly op: '+' | '-' | '*' | '/' | '=' | '!=' | '<' | '<=' | '>' | '>=' | 'and' | 'or';
      readonly left: Node;
      readonly right: Node;
    }
  | { readonly kind: 'list'; readonly items: readonly Node[] }
  | {
      readonly kind: 'range';
      readonly startOpen: boolean;
      readonly endOpen: boolean;
      readonly start: Node;
      readonly end: Node;
    }
  | { readonly kind: 'in'; readonly value: Node; readonly candidates: Node }
  | { readonly kind: 'call'; readonly name: string; readonly args: readonly Node[] };

/** 单元格谓词(DMN 决策表的一格):`-` 任意、`<10`、`[1..5]`、`"A","B"` 析取 */
export type UnaryTest =
  | { readonly kind: 'any' }
  | { readonly kind: 'compare'; readonly op: '=' | '!=' | '<' | '<=' | '>' | '>='; readonly operand: Node }
  | { readonly kind: 'range'; readonly node: Extract<Node, { kind: 'range' }> }
  | { readonly kind: 'disjunction'; readonly tests: readonly UnaryTest[] };