2015-03-04 12:20:18 +00:00
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module Assembler6502
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class SymbolTable
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##### Custom Exceptions
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class InvalidScope < StandardError; end
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class UndefinedSymbol < StandardError; end
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class CantExitScope < StandardError; end
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####
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## Initialize a symbol table that begins in global scope
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def initialize
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@symbols = {
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:global => {}
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}
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@anonymous_scope_number = 0
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@scope_stack = [:global]
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end
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####
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## Define a new scope, which can be anonymous or named
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## and switch into that scope
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def enter_scope(name = nil)
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name = generate_name if name.nil?
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name = name.to_sym
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scope = current_scope
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if scope.has_key?(name)
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path_string = generate_scope_path(path_ary)
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fail(InvalidScope, "Scope: #{path_string} already exists")
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end
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scope[name] = {}
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@scope_stack.push(name)
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end
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####
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## Exit the current scope
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def exit_scope
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if @scope_stack.size == 1
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fail(CantExitScope, "You cannot exit global scope")
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end
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@scope_stack.pop
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end
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####
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## Define a symbol in the current scope
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def define_symbol(symbol, value)
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scope = current_scope
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scope[symbol.to_sym] = value
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end
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####
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## Resolve symbol to a value, for example:
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## scope1.scope2.variable
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## It is not nessessary to specify the root scope :global
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## You can just address anything by name in the current scope
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## To go backwards in scope you need to write the full path
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## like global.sprite.x or whatever
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def resolve_symbol(name)
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value = if name.include?('.')
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path_ary = name.split('.').map(&:to_sym)
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symbol = path_ary.pop
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path_ary.shift if path_ary.first == :global
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scope = retreive_scope(path_ary)
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scope[symbol]
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else
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scope = current_scope
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scope[name.to_sym]
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end
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if value.nil?
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fail(UndefinedSymbol, name)
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end
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value
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end
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2015-03-04 17:58:50 +00:00
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####
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## Export the symbol table as YAML
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def export_to_yaml
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@symbols.to_yaml.gsub(/(\d+)$/) do |match|
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integer = match.to_i
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sprintf("0x%.4X", integer)
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end
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end
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2015-03-04 12:20:18 +00:00
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private
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####
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## A bit more clearly states to get the current scope
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def current_scope
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retreive_scope
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end
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####
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## Retrieve a reference to a scope, current scope by default
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def retreive_scope(path_ary = @scope_stack)
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path_ary = path_ary.dup
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path_ary.unshift(:global) unless path_ary.first == :global
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path_ary.inject(@symbols) do |scope, path_component|
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new_scope = scope[path_component.to_sym]
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if new_scope.nil?
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path_string = generate_scope_path(path_ary)
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message = "Resolving scope: #{path_string} failed at #{path_component}"
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fail(InvalidScope, message) if new_scope.nil?
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end
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new_scope
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end
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end
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####
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## Generate a scope path from an array
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def generate_scope_path(path_ary)
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path_ary.join('.')
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end
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####
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## Generate an anonymous scope name
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def generate_name
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@anonymous_scope_number += 1
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"anonymous_#{@anonymous_scope_number}"
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end
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end
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end
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