Alternative parsers in package space

Jim Hester



DSC 2017 - Syntax Extensions for R

Changing base R parser is challenging

  • build consensus
  • avoid conflicts / grammar ambiguities
  • requires extensive testing

altparsers package

  • https://github.com/jimhester/altparsers
  • Multiple parsers available
    • User / package author extendable
  • Can mix parsers in same package
  • REPL(s) available for interactive use
  • Experiment in package space

tidy parser

  • No plans to use widely
  • Based on R bison parser
  • Many features from previous talk
    • raw strings:
      grepl(r"\w+")
    • glue strings:
      x <- 1; g"x = {x}"
    • native pipes:
      mtcars |> filter(hp > 150) |> select(hp, mpg)
    • list generation:
      [1, 2, 3 [5, 5, 6]]

Unquoting operators (!! and !!!)

S-expression parser

  • very simple POC
  • demonstrates use of non-native parsers

Interactive use

  • Loosely based on Ross Ihaka‚Äôs R-script
  • repl() function used to start REPL with new parser
    • repl(parse_text)
    • repl(tidy_parse_text)
    • repl(sexp_parse_text)
  • q() used to exit

Package use

  • Scripts - inst/*
  • altparsers::src() to load scripts with parser
  • export / document as normal

Demo

altparsers package

  • altparsers::src()
  • altparsers::repl()
  • Experiment with parsers in packages
  • Parsers just simple examples