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MissingLisp is a minimalist Lisp interpreter embedded in Ruby. It allows you to write and evaluate Lisp expressions with Ruby's variable names.

gem install missinglisp

$ irb
irb(main):001> require 'missinglisp'
=> true
irb(main):002> Lquote_hello_world_J
=> [:hello, :world]
irb(main):003> Ladd_1_2_3J
=> 6

Other examples can be found in the examples directory.

MissingLisp implements a subset of Lisp.

• Uses L instead of ( to open expressions
• Uses J instead of ) to close expressions
  • Note: Lfoo_barJ is tokenized as L, foo barJ. If you want to use J as closing parentheses, you must use _ to separate the token: Lfoo_bar_J
• Symbols are written as normal identifiers (e.g., add, define, lambda)
• Numbers are written as normal numbers
• Whitespace is ignored. Uses _ instead of spaces

• Lif_test_then_elseJ - Conditional expression
• Lquote_expressionJ - Returns the expression without evaluating it
• Ldefine_symbol_expressionJ - Defines a symbol in the current environment
• Llambda_Lparameters_J_bodyJ - Creates a function

MissingLisp provides several built-in functions:

• car - Returns the first element of a list
• cdr - Returns all but the first element of a list
• cons - Constructs a new list by prepending an element
• list - Creates a list from its arguments

• add - Adds numbers
• sub - Subtracts numbers
• mult - Multiplies numbers
• div - Divides numbers

• eq - Tests equality
• lt - Less than
• leq - Less than or equal
• gt - Greater than
• geq - Greater than or equal

• p - Prints values (for debugging)
• nil - An empty list

MIT