junk/hygienic2.lua

   1 --------------------------------------------------------------------------------
   2 --
   3 -- (c) Fabien Fleutot 2007, published under the MIT license.
   4 --
   5 --
   6 -- API:
   7 -- ----
   8 -- * freevars.block(ast)
   9 -- * freevars.expr(ast)
  10 -- * freevars.stat(ast)
  11 --
  12 --------------------------------------------------------------------------------
  13
  14 require 'std'
  15 require 'walk'
  16 require 'freevars'
  17
  18 -{ extension 'match' }
  19
  20 --------------------------------------------------------------------------------
  21 -- Return the string->boolean hash table of the names of all free variables
  22 -- in 'term'. 'kind' is the name of an entry in module 'walk', presumably
  23 -- one of 'expr', 'stat' or 'block'.
  24 --------------------------------------------------------------------------------
  25 local function alpha (kind, term)
  26    local cfg = { expr  = { }, stat  = { }, block = { } }
  27
  28    -----------------------------------------------------------------------------
  29    -- Monkey-patch the scope add method, so that it associates a unique name
  30    -- to bound vars.
  31    -----------------------------------------------------------------------------
  32    local scope = scope:new()
  33    function scope:add(vars)
  34       for v in values(vars) do self.current[v] = mlp.gensym(v) end
  35    end
  36
  37    -----------------------------------------------------------------------------
  38    -- Check identifiers; add functions parameters to scope
  39    -----------------------------------------------------------------------------
  40    function cfg.expr.down(x)
  41       match x with
  42       | `Splice{...} -> return 'break' -- don't touch user parts
  43       | `Id{ name } ->
  44          local alpha = scope.current[name]
  45          if alpha then x[1] = alpha end
  46       | `Function{ params, _ } -> scope:push(); scope:add (params)
  47       | _ -> -- pass
  48       end
  49    end
  50
  51    -----------------------------------------------------------------------------
  52    -- Close the function scope opened by 'down()'
  53    -----------------------------------------------------------------------------
  54    function cfg.expr.up(x)
  55       match x with `Function{...} -> scope:pop() | _ -> end
  56    end
  57
  58    -----------------------------------------------------------------------------
  59    -- Create a new scope and register loop variable[s] in it
  60    -----------------------------------------------------------------------------
  61    function cfg.stat.down(x)
  62       match x with
  63       | `Splice{...}           -> return 'break'
  64       | `Forin{ vars, ... }    -> scope:push(); scope:add(vars)
  65       | `Fornum{ var, ... }    -> scope:push(); scope:add{var}
  66       | `Localrec{ vars, ... } -> scope:add(vars)
  67       | `Repeat{ block, cond } -> -- 'cond' is in the scope of 'block'
  68          scope:push()
  69          for s in values (block) do walk.stat(cfg)(s) end -- no new scope
  70          walk.expr(cfg)(cond)
  71          scope:pop()
  72          return 'break' -- No automatic walking of subparts
  73       | _ -> -- pass
  74       end
  75    end
  76
  77    -----------------------------------------------------------------------------
  78    -- Close the scopes opened by 'up()'
  79    -----------------------------------------------------------------------------
  80    function cfg.stat.up(x)
  81       match x with
  82       | `Forin{ ... } | `Fornum{ ... } -> scope:pop() -- `Repeat has no up().
  83       | `Local{ vars, ... }            -> scope:add(vars)
  84       | _ -> -- pass
  85       end
  86    end
  87
  88    -----------------------------------------------------------------------------
  89    -- Create a separate scope for each block
  90    -----------------------------------------------------------------------------
  91    function cfg.block.down() scope:push() end
  92    function cfg.block.up()   scope:pop()  end
  93
  94    walk[kind](cfg)(term)
  95    return freevars
  96 end
  97
  98 --------------------------------------------------------------------------------
  99 -- A wee bit of metatable hackery. Just couldn't resist, sorry.
 100 --------------------------------------------------------------------------------
 101 freevars = setmetatable ({ scope=scope }, { __index = |_, k| |t| fv(k, t) })