Created
August 22, 2015 16:34
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Scheme Interpreter Essensentials
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| # run on irb as follows. | |
| # $ irb -r './type0.rb' | |
| # irb> e [:define, :f, [:lambda, [:v], ["+", :v, 1]]] | |
| # irb> e [:f 1] | |
| # => 2 | |
| # ... | |
| module Type0 | |
| Environment = Struct.new(:parent, :hash) | |
| Lambda = Struct.new(:env, :params, :exp) | |
| extend self | |
| def resolve(env, var_name) | |
| if env.parent | |
| env.hash[var_name] || resolve(env.parent, var_name) | |
| else | |
| env.hash[var_name] | |
| end | |
| end | |
| def apply(lambda, *args) | |
| eval(Environment.new(lambda.env, lambda.params.zip(args).to_h), lambda.exp) | |
| end | |
| def call_ruby_method(method_name, receiver, *args) | |
| receiver.send(method_name, *args) | |
| end | |
| def eval(env, exp) | |
| case exp | |
| when Numeric, String, TrueClass, FalseClass | |
| exp | |
| when Symbol | |
| resolve(env, exp) | |
| when Array | |
| case exp[0] | |
| when :lambda | |
| Lambda.new(env, exp[1], exp[2]) | |
| when :define | |
| env.hash[exp[1]] = eval(env, exp[2]) | |
| when :if | |
| eval(env, exp[1]) ? eval(env, exp[2]) : eval(env, exp[3]) | |
| when String | |
| call_ruby_method(*exp.map{|e| eval(env, e)}) | |
| else | |
| apply(*exp.map{|e| eval(env, e)}) | |
| end | |
| end | |
| end | |
| end | |
| def e(exp) | |
| $env ||= Type0::Environment.new(nil, {}) | |
| Type0.eval($env, exp) | |
| end |
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