@fink/prattler/expressions.js

A generic Pratt/top down operator precedence parser.

import { add_error } from "./errors.js";
export const auto = {
  auto: true
};
export const error_nud = ctx => {
  const {
    curr_token
  } = ctx;
  const {
    value
  } = curr_token;
  return add_error(ctx, `Unexpected token \`${value}\` at start of expression.`, curr_token);
};
export const error_led = ctx => {
  const {
    curr_token
  } = ctx;
  const {
    value
  } = curr_token;
  return add_error(ctx, `Cannot use \`${value}\` as an infix operator.`, curr_token);
};
export const left_binding = token_type => ({
  token_type,
  nud: () => error_nud,
  lbp: lbp => () => lbp,
  led: () => error_led
});
export const non_binding = token_type => ({
  token_type,
  nud: () => error_nud,
  lbp: () => () => 0,
  led: () => error_led
});
export const add_expr = (expr_builder, lbp_value) => ({
  expr_builders,
  ...ctx
}) => {
  const {
    next_lbp,
    lbps,
    nuds,
    leds
  } = expr_builders;

  let _do_result;

  ˆmatch_2: {
    const ˆvalue_1 = lbp_value;

    if (ˆvalue_1 === auto) {
      _do_result = next_lbp;
      break ˆmatch_2;
    }

    {
      _do_result = lbp_value;
      break ˆmatch_2;
    }
  }

  const final_lbp_value = _do_result;
  _do_result = undefined;
  const {
    token_type,
    nud,
    lbp,
    led
  } = expr_builder;
  return { ...ctx,
    expr_builders: {
      next_lbp: next_lbp + 2,
      nuds: { ...nuds,
        [token_type]: nud(final_lbp_value)
      },
      lbps: { ...lbps,
        [token_type]: lbp(final_lbp_value)
      },
      leds: { ...leds,
        [token_type]: led(final_lbp_value)
      }
    }
  };
};
export const add_ignorable = token_type => ({
  igns,
  ...ctx
}) => ({ ...ctx,
  igns: { ...igns,
    [token_type]: true
  }
});
export const add_separator = expr_builder => add_expr(expr_builder, 0);
export const add_operator = expr_builder => add_expr(expr_builder, auto);
export const add_identifier = expr_builder => add_expr(expr_builder, auto);
export const add_literal = expr_builder => add_expr(expr_builder, auto);
export const is_ignorable = (ctx, token) => ctx.igns[token.type] === true;
export const nud = ctx => {
  const {
    curr_token: {
      type
    },
    expr_builders: {
      nuds
    }
  } = ctx;
  const {
    [type]: nud_fn
  } = nuds;
  return nud_fn(ctx);
};
export const led = (ctx, left) => {
  const {
    curr_token: {
      type
    },
    expr_builders: {
      leds
    }
  } = ctx;
  const {
    [type]: led_fn
  } = leds;
  return led_fn(ctx, left);
};
export const next_lbp = (ctx, left) => {
  const {
    next_token: {
      type
    },
    expr_builders: {
      lbps
    }
  } = ctx;
  const {
    [type]: lbp_fn
  } = lbps;
  return lbp_fn(ctx, left);
};
export const init_expr_builders = () => ({
  next_lbp: 2,
  nuds: {},
  lbps: {
    end: () => 0
  },
  leds: {},
  igns: {}
});