Matching Tetrominos using the Zen of Lua...

Sacrifice.lua

function Sacrifice:matchTetros(tetros, col, row)
  for _, t in ipairs(tetros) do
    local i = 1
    local matches = {}
    for c = col, col + 3 do
      for r = row, row + 3 do
        local char = t:sub(i,i)
        local limb, core = (char == '*'), (char == '@')
        if (limb or core) then
          if self:match(c, r) then
            table.insert(matches, { c = c, r = r, core = core})
            if #matches >= 4 then
              return matches
            end
          end
        end
        i = i + 1
      end
    end
  end
  return nil
end

function Sacrifice:match(col, row)
  local tile = terrain:gridToTile(col, row)
  return (tile and tile.sacrifice)-- and self.ritual[tile.sacrifice])
end

function Sacrifice:performRitual()
  -- find the bounds of the ritual space
  local min_col, min_row = self.tile.col, self.tile.row
  local max_col, max_row = min_col, min_row
  for _, s in ipairs(self.ritual) do
    local col, row = s.tile.col, s.tile.row
    if col > max_col then max_col = col end
    if col < min_col then min_col = col end
    if row > max_row then max_row = row end
    if row < min_row then min_row = row end
  end
  local w_col, h_col = max_col - min_col + 1, max_row - min_row + 1
  -- try to match each Tetromino across this space
  terrain:mapRectangle(min_col, min_row, w_col, h_col, function(tile, c, r)
    for tetroTypeName, tetroType in pairs(tetrominoes) do
      local match = self:matchTetros(tetroType, c, r)
      if match then
        log:write("found " .. tetroTypeName)
      end
    end
  end)
end

tetrominoes.lua

-- O shape
local tetro_O =   "**--".. 
                  "**--"..
                  "----"..
                  "----"

-- J shape
local tetro_J1 =  "-*--".. 
                  "-*--"..
                  "**--"..
                  "----"

local tetro_J2 =  "***-".. 
                  "--*-"..
                  "----"..
                  "----"

local tetro_J3 =  "**--".. 
                  "*---"..
                  "*---"..
                  "----"

local tetro_J4 =  "*---".. 
                  "***-"..
                  "----"..
                  "----"

-- L shape
local tetro_L1 =  "*---".. 
                  "*---"..
                  "**--"..
                  "----"

local tetro_L2 =  "--*-".. 
                  "***-"..
                  "----"..
                  "----"

local tetro_L3 =  "**--".. 
                  "-*--"..
                  "-*--"..
                  "----"

local tetro_L4 =  "***-".. 
                  "*---"..
                  "----"..
                  "----"

-- I shape
local tetro_I1 =  "*---".. 
                  "*---"..
                  "*---"..
                  "*---"

local tetro_I2 =  "****".. 
                  "----"..
                  "----"..
                  "----"

-- S shape
local tetro_S1 =  "-*--".. 
                  "**--"..
                  "*---"..
                  "----"

local tetro_S2 =  "**--".. 
                  "-**-"..
                  "----"..
                  "----"

-- Z shape
local tetro_Z1 =  "*---".. 
                  "**--"..
                  "-*--"..
                  "----"

local tetro_Z2 =  "-**-".. 
                  "**--"..
                  "----"..
                  "----"

-- T shape
local tetro_T1 =  "*---".. 
                  "**--"..
                  "*---"..
                  "----"

local tetro_T2 =  "-*--".. 
                  "***-"..
                  "----"..
                  "----"

local tetro_T3 =  "-*--".. 
                  "**--"..
                  "-*--"..
                  "----"

local tetro_T4 =  "***-".. 
                  "-*--"..
                  "----"..
                  "----"

-- pack and export
return 
{ 
      O = { tetro_O },
      J = { tetro_J1, tetro_J2, tetro_J3, tetro_J4},
      L = { tetro_L1, tetro_L2, tetro_L3, tetro_L4}, 
      I = { tetro_I1, tetro_I2},
      S = { tetro_S1, tetro_S2},
      Z = { tetro_Z1, tetro_Z2},
      T = { tetro_T1, tetro_T2, tetro_T3, tetro_T4},
}

tetrominoes come from here, and mapRectangle comes from here :)

As for core and self.ritual - what, you want all my secrets? :P