Core additions:
- StringInputPort / StringOutputPort — open-input-string, open-output-string,
get-output-string, read/read-char/peek-char/read-line on ports
- R7RS ErrorObject class — error-object?, error-object-message,
error-object-irritants; guard and with-exception-handler now receive
ErrorObject instances instead of raw strings
- Exact rational arithmetic via Fraction — (/ 1 3) => 1/3, literal 1/3
syntax, numerator/denominator, exact/inexact conversions
- Module system — (module name (export ...) body...) and (import name) /
(import (name sym ...)) for selective import
- define-record-type now a Python special form supporting (inherit parent)
for single-inheritance with subtype predicates
- Pretty-printer — pp/pretty-print with configurable line width
Correctness:
- R7RS letrec* body semantics for internal defines — names pre-declared
before any initializer runs, enabling mutual recursion in let bodies
- string->number detects #x/#b/#o/#d and 0x/0b/0o prefixes
- show() guarantees decimal point in float output
- number->string rounds through show() for consistent float representation
Performance:
- _body_env fast path: skip scan when first body form is not define/begin
- Proc.has_defs flag: skip _body_env entirely for procs without internal defines
- Single-form body optimization: skip begin wrapper, set expr directly
Tests: 396 → 455 (+59 new tests covering all new features)
