-- Copyright 2006-2020 Mitchell. See LICENSE.
-- Forth LPeg lexer.
-- Contributions from Joseph Eib.

local lexer = require('lexer')
local token, word_match = lexer.token, lexer.word_match
local P, S = lpeg.P, lpeg.S

local lex = lexer.new('forth')

-- Whitespace.
lex:add_rule('whitespace', token(lexer.WHITESPACE, lexer.space^1))

-- Strings.
local c_str = 'c' * lexer.range('"', true, false)
local s_str = 's' * lexer.range('"', true, false)
local s_bs_str = 's\\' * lexer.range('"', true)
local dot_str = '.' * lexer.range('"', true, false)
local dot_paren_str = '.' * lexer.range('(', ')', true)
local abort_str = 'abort' * lexer.range('"', true, false)
lex:add_rule('string', token(lexer.STRING, c_str + s_str + s_bs_str + dot_str +
  dot_paren_str + abort_str))

-- Keywords.
lex:add_rule('keyword', token(lexer.KEYWORD, word_match[[
  #> #s */ */mod +loop , . .r /mod 0< 0<> 0> 0= 1+ 1- 2! 2* 2/ 2>r 2@ 2drop 2dup
  2over 2r> 2r@ 2swap :noname <# <> >body >in >number >r ?do ?dup @ abort abs
  accept action-of again align aligned allot and base begin bl buffer: c! c, c@
  case cell+ cells char char+ chars compile, constant, count cr create decimal
  defer defer! defer@ depth do does> drop dup else emit endcase endof
  environment? erase evaluate execute exit false fill find fm/mod here hex hold
  holds i if immediate invert is j key leave literal loop lshift m* marker max
  min mod move negate nip of or over pad parse parse-name pick postpone quit r>
  r@ recurse refill restore-input roll rot rshift s>d save-input sign sm/rem
  source source-id space spaces state swap to then true tuck type u. u.r u> u<
  um* um/mod unloop until unused value variable while within word xor ['] [char]
  [compile]
]], true))

-- Identifiers.
lex:add_rule('identifier', token(lexer.IDENTIFIER,
  (lexer.alnum + S('+-*=<>.?/\'%,_$#'))^1))

-- Comments.
local line_comment = lexer.to_eol(S('|\\'))
local block_comment = lexer.range('(', ')')
lex:add_rule('comment', token(lexer.COMMENT, line_comment + block_comment))

-- Numbers.
lex:add_rule('number', token(lexer.NUMBER, P('-')^-1 * lexer.digit^1 *
  (S('./') * lexer.digit^1)^-1))

-- Operators.
lex:add_rule('operator', token(lexer.OPERATOR, S(':;<>+*-/[]#')))

return lex
