Sigil (0.8.0)

Dynamic FFI

The headline feature. sigil-ffi lets you call C library functions directly from Scheme without writing any C glue code. Load shared libraries with ffi-open, look up symbols with ffi-ref, define call signatures, and invoke — all at runtime.

(import (sigil ffi))

(define lib (ffi-open "libm.so.6"))
(define c-sqrt (ffi-ref lib "sqrt" '(double) 'double))
(c-sqrt 144.0) ; => 12.0

• Callbacks: c-callback creates function pointers that call back into Scheme, enabling integration with event-driven C APIs like GUI toolkits
• Pointer finalizers: set-pointer-finalizer! attaches GC-triggered cleanup to foreign pointers (pass #f to clear)
• dyncall backend: Replaced pure-C trampolines with dyncall for portable calling convention support, including mixed int/double argument signatures used by Cairo and similar libraries

Content-Addressable Build Store

A new sigil-store package provides content-addressable storage for build artifacts. C compilation results and static libraries are cached by content hash, so unchanged native code is never recompiled. Build outputs are properly rooted for GC, and the store integrates transparently with the existing build system.

App Management

New sigil app commands for installing, updating, and removing Sigil applications from git repositories:

• sigil app install — clone a repo, resolve dependencies, bundle the app, and register any MCP servers
• sigil app list — show installed applications
• sigil app update — pull latest changes and rebuild
• sigil app remove — clean up installed app and deregister MCP servers
• sigil app rollback — revert to the previous version

Supports --scope for MCP server registration, --env and secret-env for configuration, and graceful handling of missing environment variables.

New Packages

MCP Server Improvements

• Channel servers: New (sigil mcp channel) module with helpers for building MCP channel-based servers (stdin/stdout transport)
• Server-initiated notifications: MCP servers can now push notifications to clients, declare custom capabilities, and provide instructions
• Structured logging: MCP message handling uses sigil-log with log-configure-from-args! for CLI integration
• Better error reporting: Stack traces included in MCP tool error responses

HTTP Improvements

• /json route helpers now return JSON bodies on all HTTP status codes, not just 2xx
• url-encode-value and build-query-string for proper URL query parameter encoding
• Fixed UTF-8 split across HTTP read chunk boundaries
• Fixed chunked transfer decoding for non-ASCII UTF-8 content
• Fixed Content-Length using character count instead of byte length
• Fixed partial socket writes truncating large HTTP responses
• Unix domain socket server support via unix-listen

CalDAV and iCalendar

Beyond the new sigil-caldav package, significant improvements to calendar handling:

• Timezone-aware datetime parsing with correct DST offset calculation via mktime
• Attendee parameter support for event creation
• Calendar name and timezone fields on ical-event
• RRULE recurrence expansion with RECURRENCE-ID exception suppression
• Date range filtering for non-recurring events in recurrence expansion

Formatter Performance

The code formatter was optimized from 30 seconds to under 2 seconds on large files (2800+ lines):

• Replaced struct-based tokens with raw vectors
• Inlined tokenizer hot loops with delimiter lookup table
• Zero-allocation form type matching
• Fixed tokenizer mishandling of delimiter character literals

Build System

• Content-addressable store for cached C compilation and static libraries
• Fixed build cache ignoring dependency changes
• Fixed false source file matches in module dependency resolution
• Fixed test runner dependency resolution for external packages
• Fixed build store hard-link self-copy corruption
• Hardened test runner against load errors
• Default release/prerelease configs switched to glibc dynamic linking (supporting FFI and dlopen)
• Static build configs available as release-static and prerelease-static

JMAP Improvements

• jmap-email-count for lightweight email counting without fetching messages
• jmap-download-blob for downloading JMAP blobs to files
• Batch email move support
• Fixed send compatibility issues

Performance and Code Quality

• Fixed quadratic string-join — now uses linear accumulation
• Improved list-unzip to use simultaneous traversal
• Deduplicated inspect-vector and inspect-array with shared helper
• Dict-based lookups in diagnostic module and watch module for faster type-guard and mtime resolution

Bug Fixes

• Fixed crash when format displays bignum values
• Fixed segfault from unbounded macro export recursion
• Fixed preemptive yield escaping through sigil_apply boundaries
• Fixed string->list to properly decode UTF-8 characters
• Fixed string-join overflow with large lists
• Fixed double-encoded UTF-8 in build output and diagnostics
• Fixed YAML encoder to handle Sigil arrays
• Raised module binding limit from 2048 to 4096
• Fixed async stdin handling for MCP servers (pipe detection, fd-waiter integration)
• Fixed char-ready? for pipes with async-aware stdin polling
• Added Scheme module definition for sigil-tls package
• Fixed Windows cross-compilation: fcntl/FD_CLOEXEC guards replaced with SetHandleInformation
• Fixed OpenBSD cross-compilation: setvbuf workaround for opaque FILE struct in Zig headers
• Fixed OpenBSD executable path resolution, poll fd limit, and partial write handling
• Set FD_CLOEXEC on TCP sockets to prevent child process inheritance