-- This is a simple and somewhat stupid example of how to switch
-- lexers dynamically. Behind a V, X and Y are the only reserved
-- keywords. In normal conditions, X and Y aren't keywords and can be
-- used as variables.

-{ block:
   require 'lexer'
   local my_lexer = lexer.lexer:clone() -- no keywords
   my_lexer:add{"X", "Y"}
   mlp.lexer:add "V"

   function num(lx)
      local a = lx:next()
      assert(a.tag=='Number')
      return a
   end
      
   my_parser = gg.list{
      gg.multisequence{
         { "X", num, builder = |x| `Table{ x[1], +{0} } },
         { "Y", num, builder = |y| `Table{ +{0}, y[1] } },
         default = gg.sequence{ mlp.id, builder = |x| `Pair{ `String{x[1][1]},`True } } },
      separators = { ',', ';' },
      builder = function(l) l.tag='Table'; return l end }

   mlp.expr:add{ "V", gg.with_lexer(my_lexer, my_parser), builder = unpack } }

-- Use the special lexer:
foo = V X 1, Y 2, X 3, 
      for, foo, in, tag, function -- check that these aren't keywords in my_lexer

-- Use X and Y as Id, in the unpolluted lexer:
print "Vector:"
X = table.tostring(foo, 60)
print (X)

print "Sum:" -- Ready for a functional one-liner? :)
Y = |v| table.ifold (|a,b| table.imap (|c,d| c+d, a, b), {0,0}, v) 
table.print (Y(foo))