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n65/lib/symbol_table.rb

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2015-03-04 12:20:18 +00:00
module Assembler6502
class SymbolTable
##### Custom Exceptions
class InvalidScope < StandardError; end
class UndefinedSymbol < StandardError; end
class CantExitScope < StandardError; end
####
## Initialize a symbol table that begins in global scope
def initialize
@symbols = {
:global => {}
}
@anonymous_scope_number = 0
@scope_stack = [:global]
end
####
## Define a new scope, which can be anonymous or named
## and switch into that scope
def enter_scope(name = nil)
name = generate_name if name.nil?
name = name.to_sym
scope = current_scope
if scope.has_key?(name)
path_string = generate_scope_path(path_ary)
fail(InvalidScope, "Scope: #{path_string} already exists")
end
scope[name] = {}
@scope_stack.push(name)
end
####
## Exit the current scope
def exit_scope
if @scope_stack.size == 1
fail(CantExitScope, "You cannot exit global scope")
end
@scope_stack.pop
end
####
## Define a symbol in the current scope
def define_symbol(symbol, value)
scope = current_scope
scope[symbol.to_sym] = value
end
####
## Resolve symbol to a value, for example:
## scope1.scope2.variable
## It is not nessessary to specify the root scope :global
## You can just address anything by name in the current scope
## To go backwards in scope you need to write the full path
## like global.sprite.x or whatever
def resolve_symbol(name)
value = if name.include?('.')
path_ary = name.split('.').map(&:to_sym)
symbol = path_ary.pop
path_ary.shift if path_ary.first == :global
scope = retreive_scope(path_ary)
scope[symbol]
else
scope = current_scope
scope[name.to_sym]
end
if value.nil?
fail(UndefinedSymbol, name)
end
value
end
####
## Export the symbol table as YAML
def export_to_yaml
@symbols.to_yaml.gsub(/(\d+)$/) do |match|
integer = match.to_i
sprintf("0x%.4X", integer)
end
end
2015-03-04 12:20:18 +00:00
private
####
## A bit more clearly states to get the current scope
def current_scope
retreive_scope
end
####
## Retrieve a reference to a scope, current scope by default
def retreive_scope(path_ary = @scope_stack)
path_ary = path_ary.dup
path_ary.unshift(:global) unless path_ary.first == :global
path_ary.inject(@symbols) do |scope, path_component|
new_scope = scope[path_component.to_sym]
if new_scope.nil?
path_string = generate_scope_path(path_ary)
message = "Resolving scope: #{path_string} failed at #{path_component}"
fail(InvalidScope, message) if new_scope.nil?
end
new_scope
end
end
####
## Generate a scope path from an array
def generate_scope_path(path_ary)
path_ary.join('.')
end
####
## Generate an anonymous scope name
def generate_name
@anonymous_scope_number += 1
"anonymous_#{@anonymous_scope_number}"
end
end
end