Peggy proposition: Tagged template parser with auto-vectorization of template arguments

tagged-vector-adder.pegjs

{{
  function add(left, right) {
    if (typeof left === 'number') {
      if (typeof right === 'number') {
        return left + right;
      } else {
        return right.map(r => left + r);
      }
    } else {
      if (typeof right === 'number') {
        return left.map(l => l + right);
      } else {
        return left.map((l, i) => l + right[i]);
      }
    }
  }
}}

Start
  = Expression

Expression
  = left: Value '+' right: Value { return add(left, right); }

Value
  = Int
  / FormattedTemplateArgument

Int
  = [0-9]+ { return parseInt(text(), 10); }

FormattedTemplateArgument
  = arg: €TemplateArgument { return typeof arg === 'number' ? arg : new Float64Array(arg) }

/**
Above €TemplateArgument is a new magic pattern that accepts the "hole" left by ${arg} inside backquotes and passes in the value as is.

Examples:
parse`1+2`
// Evaluates to 3.

parse`5+${3}`
// Evaluates to 8.

parse`5+${[1, 2, 3]}`
// Evaluates to Float64Array(3) [ 6, 7, 8 ]
*/