logger

Simple structured logging for CHICKEN Scheme with per-module level control.

logger

Description

A lightweight logging library that provides:

Four log levels: debug, info, warn, error
Per-module log level control
Module-local logging functions via logger/install macro
Text and JSON output formats
Configurable output port
ISO 8601 timestamps

Author

Rolando Abarca

Repository

https://forgejo.rolando.cl/cpm/logger-egg

Requirements

srfi-1
medea

Documentation

Quick Start

(import logger)

;; Basic logging (uses GLOBAL module name)
(logger/d "debug message")
(logger/i "info message")
(logger/w "warning message")
(logger/e "error message")

;; Messages can be concatenated
(logger/i "user " user-id " logged in")

Output:

 2026-01-18T19:07:51Z [INFO] [GLOBAL] info message

Per-Module Logging

Use logger/install inside a module to create local d, i, w, e functions that automatically tag logs with the module name:

(module my-app
  (do-stuff)
  (import scheme chicken.base logger)

  (logger/install my-app)

  (define (do-stuff)
    (i "doing stuff")    ;; tagged as [my-app]
    (d "details...")))

Output:

 2026-01-18T19:07:51Z [INFO] [my-app] doing stuff
 2026-01-18T19:07:51Z [DEBUG] [my-app] details...

API Reference

Parameters

[parameter] logger/level

Global log level. Messages below this priority are suppressed. Default: 'debug.

Valid values: 'debug, 'info, 'warn, 'error, 'none

;; Set global level to info (hides debug messages)
(logger/level 'info)

;; Get current level
(logger/level)  ; => 'info

[parameter] logger/output

Output port for log messages. Default: (current-output-port).

(import chicken.file.posix)

;; Log to a file
(define log-port (open-output-file "app.log"))
(logger/output log-port)

;; Log to stderr
(import chicken.port)
(logger/output (current-error-port))

[parameter] logger/format

Output format. Default: 'text.

'text: Human-readable format: TIMESTAMP [LEVEL] [MODULE] message
'json: JSON format: {"ts":N,"level":"...","module":"...","message":"..."}

;; Text format (default)
(logger/format 'text)
;; Output: 2026-01-18T19:07:51Z [INFO] [GLOBAL] message

;; JSON format
(logger/format 'json)
;; Output: {"ts":1737226071,"level":"info","module":"GLOBAL","message":"message"}

[parameter] logger/module-levels

Alist of per-module log levels. Use logger/set-module-level! to modify.

Procedures

[procedure] (logger/log module-name level msg . rest)

Core logging function. Logs a message if level meets or exceeds the effective level for module-name.

module-name: Symbol identifying the module.
level: Log level symbol: 'debug, 'info, 'warn, or 'error.
msg: Message string or value.
rest: Additional values to concatenate to the message.

(logger/log 'my-module 'info "Processing item " item-id)

[procedure] (logger/d msg . rest)
[procedure] (logger/i msg . rest)
[procedure] (logger/w msg . rest)
[procedure] (logger/e msg . rest)

Convenience functions for logging at debug, info, warn, and error levels respectively. Uses 'GLOBAL as the module name.

(logger/d "debug details")
(logger/i "informational message")
(logger/w "warning!")
(logger/e "error occurred: " error-msg)

[procedure] (logger/set-module-level! module-name level)

Set the log level for a specific module. This overrides the global logger/level for that module.

;; Only show warnings and errors from noisy-module
(logger/set-module-level! 'noisy-module 'warn)

;; Show all messages from important-module even if global level is higher
(logger/set-module-level! 'important-module 'debug)

[procedure] (logger/disable-module! module-name)

Disable all logging for a specific module. Equivalent to (logger/set-module-level! module-name 'none).

(logger/disable-module! 'noisy-module)

Macros

[syntax] (logger/install module-name)

Installs module-local logging functions d, i, w, and e that automatically tag messages with module-name.

Must be called at the top level of a module, after imports.

(module my-component
  (initialize shutdown)
  (import scheme chicken.base logger)

  (logger/install my-component)

  (define (initialize)
    (i "initializing...")
    (d "loading config"))

  (define (shutdown)
    (i "shutting down")))

Log Levels

Levels from lowest to highest priority:

debug: Detailed information for debugging. Priority: 0
info: General informational messages. Priority: 1
warn: Warning conditions. Priority: 2
error: Error conditions. Priority: 3
none: Disables logging entirely. Priority: 999

Messages are logged only if their level priority is greater than or equal to the effective level for the module.

Examples

Application with Multiple Modules

;;; main.scm
(import scheme chicken.base logger)
(import my-db my-http)

;; Set global level to info
(logger/level 'info)

;; But show debug messages from database module
(logger/set-module-level! 'my-db 'debug)

;; Suppress http module unless errors
(logger/set-module-level! 'my-http 'error)

(db-connect "localhost")
(http-serve 8080)

;;; my-db.scm
(module my-db
  (db-connect)
  (import scheme chicken.base logger)

  (logger/install my-db)

  (define (db-connect host)
    (i "connecting to " host)
    (d "using default port 5432")
    ;; ...
    (i "connected")))

;;; my-http.scm
(module my-http
  (http-serve)
  (import scheme chicken.base logger)

  (logger/install my-http)

  (define (http-serve port)
    (i "starting server on port " port)  ;; suppressed
    (d "debug info")                      ;; suppressed
    ;; ...
    ))

JSON Logging for Production

(import logger chicken.file.posix)

;; Configure for production
(logger/format 'json)
(logger/level 'info)
(logger/output (open-output-file "/var/log/myapp.log"))

(logger/i "application started")
;; {"ts":1737226071,"level":"info","module":"GLOBAL","message":"application started"}

License

BSD-3-Clause

Version History

0.0.2: Initial release.