Module: Jade::Codegen::Transforms::FoldShape

Extended by:
Helpers, FoldShape
Included in:
FoldShape
Defined in:
lib/jade/codegen/transforms/fold_shape.rb

Constant Summary collapse

ACC_NAME = 
'__fold_acc__'

Constants included from Helpers

Helpers::NATIVE_RUBY_CLASSES

Instance Method Summary collapse

Methods included from Helpers

data_define, dict_constraints, dict_synthetic_name, fn_constraints, fn_impl_synthetic_name, generate_many, generate_node, impl_synthetic_name, param_synthetic_name, resolve_callee_symbol, ruby_classes_for_type, to_qualified

Instance Method Details

#generate_body(shape, registry) ⇒ Object

Emits ‘xs.reverse.reduce(BASE) { |acc, head| COMBINE’ }‘. The `reverse` gives right-associative combine order regardless of the combiner’s algebraic properties. Task effects are unaffected by build order — only the final Task chain shape determines run-time behavior.



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# File 'lib/jade/codegen/transforms/fold_shape.rb', line 64

def generate_body(shape, registry)
  shape => { list_arg:, base:, head_name:, combine:, self_call: }

  base_code = generate_node(base, registry)
  combine_code = substitute(combine, self_call)
    .then { generate_node(it, registry) }

  "#{list_arg}.reverse.reduce(#{base_code}) " \
    "{ |#{ACC_NAME}, #{head_name}| #{combine_code} }"
end

#shape_for(body, self_sym, param_names, registry) ⇒ Object

The right-fold shape:

def f(xs) ->
  case xs
    of []          -> BASE          (no self-call)
    of [h | rest]  -> COMBINE       (exactly one f(rest), strict)

Returns a shape hash, or nil if the body doesn’t match.



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# File 'lib/jade/codegen/transforms/fold_shape.rb', line 18

def shape_for(body, self_sym, param_names, registry)
  return nil unless param_names.size == 1

  sig = [self_sym, 1]
  expr = unwrap_body(body)
  return nil unless expr.is_a?(AST::CaseOf)
  return nil unless expr.branches.size == 2

  list_arg = param_names.first
  return nil unless subject_is_arg?(expr.expression, list_arg)

  empty_branch = expr.branches.find { empty_list_pattern?(it.pattern) }
  cons_branch = expr.branches.find { cons_pattern?(it.pattern) }
  return nil unless empty_branch && cons_branch
  return nil if SelfCall.contains_self_call?(
    empty_branch.body, sig, registry
  )

  head_name = head_binding_name(cons_branch.pattern)
  rest_name = rest_binding_name(cons_branch.pattern)
  return nil unless head_name && rest_name

  calls = strict_self_calls(cons_branch.body, sig, registry)
  return nil unless calls&.size == 1

  call = calls.first
  return nil unless call.args.size == 1

  arg = call.args.first
  return nil unless arg in AST::VariableReference(name: ^rest_name)
  return nil unless rest_used_only?(cons_branch.body, rest_name, call)

  {
    list_arg: list_arg,
    base: empty_branch.body,
    head_name: head_name,
    combine: cons_branch.body,
    self_call: call,
  }
end