R6RS Scheme in Go

This Scheme implementation provides mostly R6RS compliant scheme written in Go. The system has a compiler that translates the scheme program into a byte code and a virtual machine that executes the code. It will implement all necessary Scheme features, including tail calls and continuations.

The compiler implements a simple API for processing S-expressions. The API gives a clean and high-level abstraction, for example, configuration file parsing, data encoding and decoding, and other structured data operations.

Language

The implementation follows the R6RS specification but makes the following non-compliant design decisions:

• The language is type aware and the compiler uses type inference to decide types for all expressions. The root of the type tree is any which is the supertype of all types. Please, see the type tree definition below.
• Numeric tower:
  • Has exact and inexact integer and floating point types. The exact numbers use Go's big.Int and big.Float types and inexact numbers use int64 and float64 respectively
  • Operations between exact and inexact numbers generate converts to exact values (int64 + big.Int = big.Int), when the R6RS specifies that the result should be inexact.
• Global definitions are final and can't be redefined. However, it is possible to set their values if the new values are type-compatible with the variable definition. You can assing values of same type or subtype to a global variable.
• The define-constant syntax defines constant variables which can't be redefined.
• Several unary (pair?, null?, zero?, car, cdr, not) and binary (cons, +, -, *, /, =, <, >, <=, >=) functions are inlined and implemented as VM bytecode operands. The runtime also implements the funtions as procedures so it is possible to apply them to arguments.

Types

The compiler uses type inference to resolve types for all expressions. The type hierarchy is as follows:

Any
  |
  +-- Nil
  |
  +-- Boolean
  |
  +-- String
  |
  +-- Character
  |
  +-- Symbol
  |
  +-- Vector
  |
  +-- Bytevector
  |
  +-- Number
  |     |
  |     +-- ExactInteger (big.Int)
  |     |     |
  |     |     +-- InxactInteger (int64)
  |     |
  |     +-- ExactFloat (big.Float)
  |           |
  |           +-- InxactFloat (float64)
  |
  +-- Lambda(Type...) Type
  |
  +-- Pair(Type, Type)

TODO

• Shortlist
  • Top-levels with (import)
  • Library local symbols
• API
  • Marshal / unmarshal
• VM
  • Tail-call within same function as jump
  • 5.8. Multiple return values
  • Error handlers
  • Call with current continuation
• Compiler
  • 7.1. Library form
    • import/export
    • rename
    • xxx
  • 8. Top-level programs
  • 9. Primitive syntax
    • 9.2. Macros
  • 10. Expansion process
• 11. Base Library (rnrs base (6))
  • 11.2.2. Syntax definitions
    • define-syntax
  • 11.3. Bodies
  • 11.7. Arithmetic
    • complex?
    • real?
    • rational?
    • real-valued?
    • rational-valued?
    • integer-valued?
    • inexact
    • exact
    • finite?
    • infinite?
    • nan?
    • abs
    • div-and-mod
    • div
    • div0-and-mod0
    • div0
    • mod0
    • gcm
    • lcm
    • numerator
    • denominator
    • floor
    • ceiling
    • truncate
    • round
    • rationalize
    • exp
    • log
    • sin
    • cos
    • tan
    • asin
    • acos
    • atan
    • sqrt
    • exact-integer-sqrt
    • make-rectangular
    • make-polar
    • real-part
    • imag-part
    • magnitude
    • angle
    • number->string
    • string->number
  • 11.16. Iteration
    • Named let
  • 11.17. Quasiquotation
    • quasiquote
    • unquote
    • unquote-splicing
• R6RS Libraries
  • 1. Unicode (rnrs unicode (6))
    • char-foldcase
    • char-general-category
    • string-titlecase
    • string-foldcase
    • string-normalize-nfd
    • string-normalize-nfkd
    • string-normalize-nfc
    • string-normalize-nfkc
  • 2. Bytevectors (rnrs bytevectors (6))
    • endianness
    • native-endianness
    • bytevector-u8-set!
    • bytevector-s8-set!
    • bytevector->u8-list
    • u8-list->bytevector
    • xxx
  • 3. List utilities (rnrs lists (6))
    • find
    • for-all
    • exists
    • filter
    • partition
    • fold-left
    • fold-right
    • remp
    • remove
    • remv
    • remq
    • cons*
  • 4. Sorting (rnrs sorting (6))
    • list-sort
    • vector-sort
    • vector-sort!
  • 5. Control structures (rnrs control (6))
    • when
    • unless
    • do
    • case-lambda
  • 6. Records
  • 7. Exceptions and conditions
  • 8. I/O
    • 8.2. Port I/O (rnrs io ports (6))
    • 8.3. Simple I/O (rnrs io simple (6))
      • eof-object
      • eof-object?
      • call-with-input-file
      • call-with-output-file
      • current-input-port
      • with-input-from-file
      • with-output-to-file
      • open-input-file
      • open-output-file
      • close-input-port
      • close-output-port
      • read-char
      • peek-char
      • read
      • write-char
  • 9. File system (rnrs files (6))
  • 10. Command-line access and exit values (rnrs programs (6))
  • 11. Arithmetic
  • 12. syntax-case (rnrs syntax-case (6))
  • 13. Hashtables (rnrs hashtables (6))
  • 14. Enumerations (rnrs enums (6))
  • 15. Composite library (rnrs (6))
  • 16. Eval (rnrs eval (6))
  • 17. Mutable pairs (rnrs mutable-pairs (6))
  • 18. Mutable strings (rnrs mutable-strings (6))
    • string-set!
    • string-fill!
  • 19. R5RS compatibility (rnrs r5rs (6))
    • exact->inexact
    • inexact->exact
    • quotient
    • remainder
    • modulo
    • delay
    • force
    • null-environment
    • scheme-report-environment