shin1m / lilis

A LIttle LISp interpreter

lilis

lilis is a LIttle LISp interpreter. This is a kind of etude for myself to learn lisp concepts and how to implement them.

It has a minimal set of features:

• Symbols
• Pairs
• Quotes
• Quasi quotes
• Lambda closures
• Static scoping
• Tail calls
• Macros
• Modules
• Delimited continuations
• Not implemented yet: integers, floats, strings

Builtins

(lambda ARGUMENTS EXPRESSIONS)

ARGUMENTS: (SYMBOL*)
    | (SYMBOL+ . REST)
    | REST
REST: SYMBOL
EXPRESSIONS: EXPRESSION*

Instantiates a new lambda closure.

(begin EXPRESSIONS)

Evaluates EXPRESSIONS in order. The result of the last EXPRESSION is the result of this form.

(define SYMBOL EXPRESSION)

Evaluates EXPRESSION and bind it to SYMBOL. The bound value is the result of this form.

(set! SYMBOL EXPRESSION)

Evaluates EXPRESSION and assign it to SYMBOL. The assigned value is the result of this form.

(define-macro SYMBOL ARGUMENTS EXPRESSIONS)

Defines a new macro and bind it to SYMBOL.

(export SYMBOL)

Exports a binding to SYMBOL from the current module.

(import SYMBOL)

Loads a module named SYMBOL.lisp and imports all exported symbols from the module into the current scope.

(if CONDITION THEN [ELSE])

CONDITION: EXPRESSION
THEN: EXPRESSION
ELSE: EXPRESSION

If CONDITION evaluates to other than (), evaluates THEN and the result of it is the result of this form. Otherwise, evaluates ELSE and the result of it is the result of this form.

(eq? x y)

x: OBJECT
y: OBJECT

If x and y are identical, returns a value other than (). Otherwise, returns ().

(pair? x)

x: OBJECT

If x is a PAIR object, returns a value other than (). Otherwise, returns ().

(cons head tail)

head: OBJECT
tail: OBJECT

Instantiates a new PAIR object with car part head and cdr part tail.

(car x)

x: PAIR

Returns the car part of x.

(cdr x)

x: PAIR

Returns the cdr part of x.

(gensym)

Instantiates a new unique SYMBOL object.

(module)

Instantiates a new anonymous MODULE object.

(read [eof])

eof: OBJECT

Reads an S-expression from the standard input stream. When end of file is reached before an expression, returns eof if given or (). Otherwise, returns an expression read from the stream.

(eval expression module)

expression: OBJECT
module: MODULE

Evaluates expression with module. module is a MODULE object instantiated by (module). Returns the result of evaluation.

(print values...)

values: list of OBJECT

Prints values in one line. Returns ().

(call-with-prompt tag handler thunk)

tag: OBJECT
handler: (_ continuation values...)
    continuation: CONTINUATION
    values: list of OBJECT
thunk: (_)

Sets up a new prompt tagged with tag and calls thunk. When (abort-to-prompt tag values...) is evaluated during the execution of thunk, it calls (handler continuation values...). continuation is a CONTINUATION object. (continuation value) resumes the execution of thunk at the point where (abort-to-prompt tag values...) is evaluated passing value as the result. If handler reaches the end, returns the result of it. If the execution of thunk reaches the end, returns the result of it.

(abort-to-prompt tag values...)

tag: OBJECT
values: list of OBJECT

Instantiates a new CONTINUATION object continuation delimited by the closest prompt tagged with tag and calls (handler continuation values). Returns value of (continuation value).

(error message)

message: OBJECT

Instantiates a new ERROR object with a message message.

(catch continuation error)

continuation: CONTINUATION
error: ERROR

Extracts call stack of continuation and append them to error as backtrace. catch is also used as the tag for system errors. So system errors can be handled by (call-with-prompt catch ...). Returns error.

How to Build and Run Tests

mkdir build
cd build
cmake ..
cmake --build.
ctest

License

The MIT License (MIT)

Copyright (c) 2018-2021 Shin-ichi MORITA

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.