mruby-proc-binding

This mrbgem provides a binding method for Proc objects in mruby. This method returns a Binding object, which allows you to inspect and manipulate the lexical scope (local variables and self) of the Proc from which it was obtained.

Usage Examples

Here's how you can use mruby-proc-binding:

Getting a Binding

First, obtain a Binding object from a Proc:

def create_proc
  a = 10
  b = 20
  ->(c) { a + b + c } # A sample proc
end

my_proc = create_proc
# Create a proc that takes one argument (c) and closes over a and b.
# Note: For the binding to capture local variables like 'a' and 'b',
# they must be referenced by a Proc defined in the same scope.
# A simple `proc {}` or `->{}` might not capture them as expected
# unless they are used within that proc.
# To ensure 'a' and 'b' are part of the environment captured by the binding
# from `my_proc.binding`, we ensure `my_proc` itself uses them or is defined
# in a scope where they are present and then `binding` is called on a proc
# that has access to this environment.

# Let's define a new proc specifically for getting a binding
# that captures the desired local variables.
local_var_scope_proc = nil
a_val = 1
b_val = 2
local_var_scope_proc = -> {
  # 'a_val' and 'b_val' are now in this proc's lexical scope
}
bind = local_var_scope_proc.binding

Inspecting Local Variables

You can list the names of local variables within the proc's scope:

# Continuing from the previous example:
# Variables 'a_val', 'b_val', and 'local_var_scope_proc' are expected.
p bind.local_variables
# Expected output (order may vary):
# => [:a_val, :b_val, :local_var_scope_proc, :bind]
# Note: The binding itself and other variables defined in the
# same scope might also be listed.

Getting Local Variable Values

Retrieve the value of a specific local variable:

p bind.local_variable_get(:a_val)  # => 1
p bind.local_variable_get(:b_val)  # => 2

Setting Local Variable Values

You can also modify the values of local variables within the binding's scope:

bind.local_variable_set(:a_val, 100)
p bind.local_variable_get(:a_val)  # => 100

# This also affects evaluation within the binding
p bind.eval("a_val + b_val")          # => 102 (100 + 2)

Evaluating Code

Execute arbitrary Ruby code within the binding's context:

# Define some variables in a scope
def get_binding_for_eval
  x = 5
  y = 10
  proc {}.binding # Create a binding in this scope
end

eval_bind = get_binding_for_eval
p eval_bind.eval("x * y")      # => 50
p eval_bind.eval("self")       # Shows the receiver of the proc

Getting Source Location

If mruby-proc-ext is also available, you can get the source location of a proc:

# Assuming __FILE__ is "test.rb" and this line is line 50
my_lambda = -> { } # This proc is defined at [__FILE__, __LINE__]
location_binding = my_lambda.binding

# This requires mruby-proc-ext
if location_binding.respond_to?(:source_location)
  p location_binding.source_location # => ["test.rb", 50] (approximately)
else
  puts "Binding#source_location not available. Is mruby-proc-ext included?"
end

A more robust example for capturing variables for Proc#binding:

def execution_binding
  name = "Ruby"
  # The proc must be created in the scope where variables exist
  # and it doesn't necessarily need to *use* them for them to be available in the binding.
  # However, the most reliable way to ensure they are part of the environment
  # is if the proc is created in that environment.
  binding_proc = proc {} # This proc is created in the current scope
  binding_proc.binding   # Returns a binding for this scope
end

b = execution_binding
p b.local_variables.sort  # => [:b, :binding_proc, :name] (or similar)
p b.local_variable_get(:name) # => "Ruby"
b.local_variable_set(:name, "mruby")
p b.eval("name") # => "mruby"

Dependencies

This mrbgem has the following dependencies:

mruby-binding: Provides the core Binding object functionality. This gem is a prerequisite.
mruby-proc-ext: Required for the Binding#source_location method. If mruby-proc-ext is not included in your mruby build, the source_location method may not be available on binding objects, or it might return nil.

License

MIT

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