rename file & add copyright

prol.rb

@@ -0,0 +1,123 @@
+# It's a minimal lisp interpreter written in Ruby-lang
+# Author: @vonhyou
+# Start at: Apr. 10, 2021
+
+##### Parser
+# :parse
+# :tokenize
+# :read_tokens
+# :atom
+#####
+
+def parse(program)
+  read_tokens(tokenize(program))
+end
+
+def tokenize(program)
+  # Convert scripts to token lists
+  program.gsub('(', ' ( ').gsub(')', ' ) ').split
+end
+
+def make_list(tokens)
+  lst = []
+  lst << read_tokens(tokens) while tokens[0] != ')'
+  tokens.shift
+  lst
+end
+
+def read_tokens(tokens)
+  # read expressions from token
+  raise SyntaxError, 'Unexpected EOF' if tokens.empty?
+
+  case token = tokens.shift
+  when '('
+    make_list tokens
+  when ')'
+    raise SyntaxError, "Unexpected ')'"
+  else
+    atom token
+  end
+end
+
+def atom(token)
+  # Analyse numbers and symbols
+  case token
+  when /\d/
+    (token.to_f % 1).positive? ? token.to_f : token.to_i
+  else
+    token.to_sym
+  end
+end
+
+##### Environments
+
+$global_env = {
+  '+': ->(args) { args.sum }, # args.inject(0, :+)
+  '-': ->(*args) { eval args.join('-') },
+  '*': ->(*args) { eval args.join('*') },
+  '/': ->(*args) { eval args.join('/') },
+  '>': ->(args) { args[0] > args[1] },
+  '<': ->(args) { args[0] < args[1] },
+  '=': ->(args) { args[0] == args[1] },
+  '>=': ->(args) { args[0] >= args[1] },
+  '<=': ->(args) { args[0] <= args[1] },
+  'min': ->(*args) { args.min },
+  'max': ->(*args) { args.max },
+  'car': ->(arr) { arr[0] },
+  'cdr': ->(arr) { arr[1..-1] },
+  'cons': ->(arr) { arr },
+  'quote': ->(arr) { arr },
+  'print': ->(arg) { p arg },
+  'begin': ->(*_args) { true }
+}
+
+##### Lisp Eval
+def lisp_eval(elem, env = $global_env)
+  if elem.instance_of? Symbol
+    env[elem]
+  elsif elem.instance_of?(Integer) || elem.instance_of?(Float)
+    elem
+  elsif elem[0] == :def
+    _, sym, exp = elem
+    env[sym] = lisp_eval(exp, env)
+  elsif elem[0] == :if
+    _, cod, if_true, if_false = elem
+    exp = lisp_eval(cod, env) ? if_true : if_false
+    lisp_eval exp, env
+  elsif elem[0] == :lambda
+    _, params, body = elem
+    ->(*args) { lisp_eval body, env.merge(Hash[params.zip(args)]) }
+  elsif elem[0] == :and
+    lisp_eval(elem[1], env) && lisp_eval(elem[2], env)
+  elsif elem[0] == :or
+    lisp_eval(elem[1], env) || lisp_eval(elem[2], env)
+  elsif elem[0] == :not
+    !lisp_eval(elem[1], env)
+  else
+    args = []
+    elem[1..-1].each { |arg| args << lisp_eval(arg, env) }
+    p lisp_eval(elem[0], env)
+    lisp_eval(elem[0], env).call args
+  end
+end
+
+$copyleft = "Copyleft (Ↄ) 2021 vonhyou@lenva.tech
+This is an open source software, you can view it's source code on github:
+https://github.com/vonhyou/lisp-interpreter\n\n"
+
+##### REPL
+def repl(prompt = 'prol ƛ>> ')
+  puts $copyleft
+  loop do
+    print prompt
+    val = lisp_eval(parse(gets.chomp))
+
+    print_value val unless val.nil? || val.instance_of?(Proc)
+  end
+end
+
+def print_value(value)
+  puts ";Value: #{value}"
+end
+
+repl