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https://github.com/vonhyou/lisp-interpreter.git
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117 lines
2.5 KiB
Ruby
117 lines
2.5 KiB
Ruby
# It's a minimal lisp interpreter written in Ruby-lang
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# Author: @vonhyou
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# Start at: Apr. 10, 2021
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##### Parser
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# :parse
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# :tokenize
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# :read_tokens
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# :atom
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#####
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def parse(program)
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read_tokens(tokenize(program))
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end
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def tokenize(program)
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# Convert scripts to token lists
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replacements = { '(' => ' ( ', ')' => ' ) ' }
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program.gsub(Regexp.union(replacements.keys), replacements)
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.split(' ')
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end
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def make_list(tokens)
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lst = []
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lst << read_tokens(tokens) while tokens[0] != ')'
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tokens.shift
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lst
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end
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def read_tokens(tokens)
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# read expressions from token
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raise SyntaxError, 'Unexpected EOF' if tokens.empty?
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token = tokens.shift
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case token
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when '('
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make_list tokens
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when ')'
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raise SyntaxError, "Unexpected ')'"
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else
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atom token
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end
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end
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def atom(token)
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# Analyse numbers and symbols
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is_integer = ->(atom) { atom.match?(/^-?\d+$/) }
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is_float = ->(atom) { atom.match?(/^(-?\d+)(\.\d+)?$/) }
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return Integer token if is_integer.call token
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return Float token if is_float.call token
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token.to_sym
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end
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##### Environments
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def generate_env
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lisp_env = {
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'+': ->(args) { args.sum }, # args.inject(0, :+)
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'-': ->(*args) { eval args.join('-') },
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'*': ->(*args) { eval args.join('*') },
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'/': ->(*args) { eval args.join('/') },
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'>': ->(args) { args[0] > args[1] },
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'<': ->(args) { args[0] < args[1] },
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'=': ->(args) { args[0] == args[1] },
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'>=': ->(args) { args[0] >= args[1] },
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'<=': ->(args) { args[0] <= args[1] },
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'min': ->(*args) { args.min },
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'max': ->(*args) { args.max },
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'car': ->(arr) { arr[0] },
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'cdr': ->(arr) { arr[1..-1] },
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'cons': ->(arr) { arr },
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'quote': ->(arr) { arr },
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'print': ->(arg) { p arg },
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'begin': ->(*_args) { true }
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}
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end
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##### Lisp Eval
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$global_env = generate_env
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def lisp_eval(elem, env = $global_env)
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if elem.instance_of? Symbol
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env[elem]
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elsif elem.instance_of?(Integer) || elem.instance_of?(Float)
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elem
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elsif elem[0] == :def
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_, sym, exp = elem
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env[sym] = lisp_eval(exp, env)
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elsif elem[0] == :if
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_, cod, if_true, if_false = elem
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exp = lisp_eval(cod, env) ? if_true : if_false
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lisp_eval exp, env
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else
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args = []
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elem[1..-1].each { |arg| args << lisp_eval(arg, env) }
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p lisp_eval(elem[0], env)
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lisp_eval(elem[0], env).call args
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end
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end
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##### REPL
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def repl(prompt='minlisp ƛ>> ')
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loop do
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print prompt
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val = lisp_eval(parse(gets.chomp))
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print_value val unless val.nil?
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end
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end
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def print_value(value)
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puts ";Value: #{value.to_s}"
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end
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# repl()
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