Class: Platform::IEL::Evaluator

Inherits:
Object
  • Object
show all
Defined in:
lib/introhive_expression_language/iel/evaluator.rb

Class Method Summary collapse

Class Method Details

.apply_fn(node, ctx) ⇒ Object

Raises:



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 54

def self.apply_fn(node, ctx)
  # Decode the function name.
  name_node = node.value.first
  raise EvaluationError.new('symbol expected', name_node) if name_node.nil?
  raise EvaluationError.new('function application requires symbol', name_node) if name_node.kind != :symbol
  symbol_name = name_node.value

  # Get the detail of this symbol from the provided context.
  detail_node = ctx[symbol_name]
  raise EvaluationError.new("function '#{symbol_name}' is not found", detail_node) if detail_node.nil?
  fn_proc = detail_node.value[:proc]
  arg_list = detail_node.value[:arg_list]

  # Create a new context overriding the provided context.
  this_ctx = EvaluationContext.new(ctx)

  # Decode the parameters and bind each to the new context.
  if arg_list.size == 1 && arg_list[0].start_with?('va_')
    # Varargs - build a list and bind as single arg
    this_ctx[arg_list[0]] = SexpParser::Node.list(node.value.drop(1).map do |arg_node|
      if arg_list[0].end_with?('__')
        arg_node
      else
        eval_node(arg_node, ctx)
      end
    end, node.source)
  else
    # Args are bound by placement and the number must match.
    raise EvaluationError.new("function '#{symbol_name}' requires #{arg_list.size} arguments but #{node.value.size - 1} are provided.", node) if arg_list.size != node.value.size - 1
    node.value.drop(1).each_with_index do |arg_node, index|
      arg_name = arg_list[index]
      this_ctx[arg_name] = if arg_name.end_with?('__')
                             arg_node
                           else
                             eval_node(arg_node, ctx)
                           end
    end
  end

  # Invoke the function.
  rv = fn_proc.call(this_ctx)
  raise EvaluationError.new("function '#{symbol_name}' does not return a node", rv) unless rv.is_a?(SexpParser::Node)
  rv
end

.deref_symbol(symbol_node, ctx) ⇒ Object

Raises:



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 48

def self.deref_symbol(symbol_node, ctx)
  target = ctx[symbol_node.value]
  raise EvaluationError.new("symbol '#{symbol_node.value}' at #{symbol_node.source} not found", target) if target.nil?
  target
end

.eval_block(node, ctx) ⇒ Object

Evaluate each item inside this “block” of code (e.g. a list) and return the last evaluated result. e.g. [

[puts "hello"]
[puts "world"]
123

] hello world

> 123



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 109

def self.eval_block(node, ctx)
  rv = nil
  node.value.each do |child_node|
    rv = Evaluator.eval_node(child_node, ctx)
  end
  rv
end

.eval_block_expr(expr, ctx) ⇒ Object 



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 17

def self.eval_block_expr(expr, ctx)
  ast = Parser.parse(expr)
  eval_block(ast, ctx)
end

.eval_expr(expr, ctx) ⇒ Object 



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 12

def self.eval_expr(expr, ctx)
  ast = Parser.parse(expr)
  eval_node(ast, ctx)
end

.eval_list_node(node, ctx) ⇒ Object 



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 33

def self.eval_list_node(node, ctx)
  # First special form - function application
  if function_application?(node, ctx)
    apply_fn(node, ctx)
  else
    SexpParser::Node.list(
        node.value.map {|child_node| eval_node(child_node, ctx)},
        node.source)
  end
end

.eval_node(node, ctx) ⇒ Object 



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 22

def self.eval_node(node, ctx)
  case node.kind
  when :list
    eval_list_node(node, ctx)
  when :symbol
    deref_symbol(node, ctx)
  else
    node
  end
end

.function_application?(node, ctx) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 44

def self.function_application?(node, ctx)
  node.kind == :list && node.value.first && node.value.first.kind == :symbol && ctx[node.value.first.value] && ctx[node.value.first.value].kind == :native_function
end

.numeric_value_of(node) ⇒ Object

Returns the numeric value of this node. It does not evaluate the node first, just returns its numeric value if possible.



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 140

def self.numeric_value_of(node)
  if node.kind == :numeric_literal
    node.value
  elsif node.kind == :string_literal
    node.value.to_f
  else
    0
  end
end

.string_value_of(node) ⇒ Object

Returns the string value of this node. It does not evaluate the node first, just returns its string value if possible.



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 152

def self.string_value_of(node)
  if node.kind == :numeric_literal
    node.value.to_s
  elsif node.kind == :string_literal
    node.value
  elsif node.kind == :list
    node.value.map {|item| string_value_of(item)}.join
  else
    ''
  end
end

.wrap_native_function(&fn) ⇒ Object

Wraps a native function so that it can be invoked in an expression. The native function MUST accept the evaluation context as its first param. The remaining params are mapped as iel mandatory args.



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# File 'lib/introhive_expression_language/iel/evaluator.rb', line 120

def self.wrap_native_function(&fn)
  arg_list = fn.parameters.drop(1).map {|_kind, name| name.to_s}

  wrapped_fn = lambda do |ctx|
    args = [ctx] + arg_list.map {|name| ctx[name]}
    fn.call(*args)
  end

  SexpParser::Node.new(
      :native_function,
      0,
      {
          proc: wrapped_fn,
          arg_list: arg_list
      }
  )
end