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----
-- Builtin / Special Form evaluation Strategy (`builtin`).
--
-- Responsible for quoting/evaluating subexpressions, instantiating and setting
-- up `Op`s, updating the current `Scope`, etc.
-- See `builtin` and `invoke` for examples.
--
-- @classmod Action
class Action
--- Action interface.
--
-- methods that have to be implemented by `Action` implementations.
-- @section interface
--- create a new instance.
--
-- @tparam Cell cell the Cell to evaluate
-- @tparam Value head the (`AST:eval`d) `head` of the Cell to evaluate
new: (@cell, @head) =>
@tag = @cell.tag
@tag\replace @
--- perform the actual evaluation.
--
-- Implementations should:
--
-- - eval or quote `tail` values
-- - perform scope effects
-- - wrap all child-results
--
-- @tparam Scope scope the active scope
-- @tparam {AST,...} tail the arguments to this expression
-- @treturn Result the result of this evaluation
eval: (scope, tail) => error "not implemented"
--- free resources
destroy: =>
--- setup or copy state from previous instance of same type.
--
-- `prev` is only passed if Action types of prev and current expression match.
-- Otherwise, or when no previous expression exists, `nil` is passed.
--
-- @tparam ?Action prev the previous Action instance
setup: (prev) =>
--- the `Cell` this Action was created for.
-- @tfield Cell cell
--- the evaluated head of `cell`.
-- @tfield AST head
--- the identity of `cell`.
-- @tfield Tag tag
--- static functions
-- @section static
--- create and setup an `Action` for a given tag, then evaluate it.
--
-- Create a new instance using `tag` and `head` and call `setup` on it.
-- If a previous instance with the same `tag` exists and has the same `head`,
-- it pass it to `setup`. Register the `Action` with `tag`, evaluate it
-- and return the `Result`.
--
-- @tparam Cell cell the `Cell` being evaluated
-- @tparam Scope scope the active scope
-- @tparam Value head the (`AST:eval`d) head of the `Cell` being evaluated
-- @treturn Result the result of evaluation
@eval_cell: (cell, scope, head) =>
last = cell.tag\last!
compatible = last and (last.__class == @) and last.head == head
L\trace if compatible
"reusing #{last} for #{cell.tag} <#{@__name} #{head}>"
else if last
"replacing #{last} with new #{cell.tag} <#{@__name} #{head}>"
else
"initializing #{cell.tag} <#{@__name} #{head}>"
action = @ cell, head
if compatible
action\setup last
else
last\destroy! if last
action\setup nil
action\eval scope, cell\tail!
__tostring: => "<#{@@__name} #{@head}>"
__inherited: (cls) => cls.__base.__tostring = @__tostring
{
:Action
}
|
