import type { CodePointSpan } from 'source-region';

export type ConcreteSyntax = Expr<{ span: CodePointSpan }>

export type Expr<A> =
| { tag: "literal", value: Literal } & A
| { tag: "list", values: Expr<A>[] } & A

export namespace ConcreteSyntax {
  export function number(value: number, span: CodePointSpan): ConcreteSyntax {
    return { tag: "literal", value: { tag: "number", value }, span };
  }

  export function identifier(value: Identifier, span: CodePointSpan): ConcreteSyntax {
    return { tag: "literal", value: { tag: "identifier", value }, span };
  }

  export function list(values: ConcreteSyntax[], span: CodePointSpan): ConcreteSyntax {
    return { tag: "list", values, span };
  }
}

export namespace Expr {
  export function number(value: number): Expr<void> {
    return { tag: "literal", value: { tag: "number", value } };
  }

  export function identifier(value: Identifier): Expr<void> {
    return { tag: "literal", value: { tag: "identifier", value } };
  }

  export function list(values: Expr<void>[]): Expr<void> {
    return { tag: "list", values };
  }

  export function show<A>(e: Expr<A>): string {
    switch (e.tag) {
      case "literal":
        return showLiteral(e.value);
      case "list":
        return `(${e.values.map(show).join(" ")})`;
    }
  }

  function showLiteral(e: Literal): string {
    switch (e.tag) {
      case "number":
        return `${e.value}`;
      case "identifier":
        return `${e.value}`;
    }
  }
}

type Literal =
| { tag: "number", value: number }
| { tag: "identifier", value: Identifier }

type Identifier = string