-- case.lua
-- Implementing a general case statement in Lua
--~ function testcase(k)
--~ 	case (k)
--~ 	  is 10,11: return 1
--~ 	  is 12: return 2
--~ 	  is 13 .. 16: return 3	  
--~ 	  else return 4
--~ 	endcase
--~ end
--
--~ function matchcase(s)
--~ 	case(s)
--~ 		matches '^hell': return 5
--~ 		matches '(%d+)%s+(%d+)',result:
--~ 			return tonumber(result[1])+tonumber(result[2])
--~ 		else return 0
--~     endcase
--~ end
local define = macro.define
local replace = macro.replace
local number = macro.number
local name = macro.name
local strmatch = string.match
local strfind = string.find

define('case',{'var'},@ do __case = var; if false then @)
define('endcase',nil,@ end; end @)

-- looks for the particular pattern {'<number>',r1,'..','<number>',r2}
-- and returns r1 and r2 if successful
-- There is a _lexical_ gotcha with r1..r2 without whitespace around '..'; Lua regards this as a malformed number
local function try_extract_range(arg)
	if arg[1] == '<number>' and arg[3]=='..' and arg[4]=='<number>' then
		return arg[2],arg[5]
	end
end

define('is',{'value',handle_parms = macro.parameter_grabber(':')}, 
	function(ls,...)
		local args = {...}
		local subst,put = macro.subst_putter()
		put('elseif')
		for i,arg in ipairs(args) do
			local r1,r2 = try_extract_range(arg)
			if r1 then
				put(replace({'r1','r2'},{number(r1), number(r2)},
					@(r1<=__case and r2>=__case)@))
			else
				put(arg); put('=='); 	put('<name>','__case')
			end
			if i < #args then
				put('or')
			end
		end
		put('then')
		return subst
	end	
	)
	
function __matches(str,pat,res)
	if not res then return strfind(str,pat)
	else
		 local tbl = {strmatch(str,pat)}
		 if #tbl > 0 then 
			_G[res] = tbl
			return true
		 end
	end
end

define('matches',{'value',handle_parms = macro.parameter_grabber(':')},
	function(ls,...)
		local args = {...}
		local subst,put = macro.subst_putter()
		put('elseif')
		put('<name>','__matches'); put('('); put('<name>','__case'); put(',')
		put(args[1])
		if #args > 1 then
			put(',')
			if args[2][1] ~= '<name>' then
				macro.error("must supply a variable name to receive captures")
			end
			put('<string>',args[2][2])
		end
		put(')')
		put('then')
		return subst
	end	
	)