HewStandard Library

Module std::misc::log

Structured, leveled logging for Hew programs (slog-style).

import std::misc::log;

Provides two surfaces:

  1. Module-level functions — convenience API using the global level/format settings, equivalent to Go's log/slog package-level functions.

  2. Logger record — a value that carries its own level and format, so multiple loggers can coexist with different settings without touching the global state.

Usage — module-level

fn main() {
    log.setup();   // set global level to INFO
    log.info("server starting");
    log.info_with("listening", [log.field_int("port", 8080), log.field("env", "prod")]);
    log.debug_with("cache miss", [log.field("key", "user:1")]);
}

Usage — Logger value

fn main() {
    let lg = log.new_logger(log.DEBUG, log.JSON);
    log.logger_info(lg, "startup", [log.field("svc", "auth")]);
    log.logger_debug(lg, "trace", [log.field_int("uid", 42)]);
}

Structured fields

Fields are key=value strings built by the helper functions:

Pass them as a Vec<string> to any *_with or logger_* function. Empty Vec is valid and equivalent to calling the plain one-arg variant.

Level constants

ERROR (0) > WARN (1) > INFO (2) > DEBUG (3) > TRACE (4)

Output formats

TEXT (0) — coloured timestamp + level + message + fields to stderr:

12:34:56.789 INFO  server starting  port=8080

JSON (1) — single-line NDJSON to stderr:

{"ts":1234567890.123,"level":"INFO","msg":"server starting","port":"8080"}

Contents

Functions

Function new_logger

pub fn new_logger(level: i64, format: i64) -> Logger

Construct a Logger with the given level threshold and output format.

level — minimum severity to emit (0=ERROR … 4=TRACE). format — log.TEXT (0) or log.JSON (1).

Function logger_level

pub fn logger_level(lg: Logger) -> i64

Return the level threshold of a Logger.

Because the Logger record's fields are not directly accessible from outside this module (cross-module record field access is not yet supported by the MIR), use this accessor when the level needs to be inspected — for example, in tests.

Function logger_format

pub fn logger_format(lg: Logger) -> i64

Return the output format of a Logger.

See logger_level for why an explicit accessor is provided.

Function field

pub fn field(key: string, val: string) -> string

Build a key=value field from two strings.

Values that contain spaces, double-quotes, backslashes, or newlines are automatically quoted so they roundtrip correctly through the log wire format. field("user", "John Doe") produces user="John Doe" on the wire and renders as user=John Doe in TEXT output.

Example

let f = log.field("env", "production");    // "env=production"
let g = log.field("user", "John Doe");     // user="John Doe"  (quoted)

Function field_int

pub fn field_int(key: string, val: i64) -> string

Build a key=N field from a string key and an i64 value.

Example

let f = log.field_int("port", 8080);  // "port=8080"

Function field_float

pub fn field_float(key: string, val: f64) -> string

Build a key=X field from a string key and an f64 value.

Example

let f = log.field_float("ratio", 0.75);  // "ratio=0.75"

Function field_bool

pub fn field_bool(key: string, val: bool) -> string

Build a key=true or key=false field.

Example

let f = log.field_bool("debug", true);  // "debug=true"

Function setup

pub fn setup()

Initialize logging at the default INFO level.

Function set_level

pub fn set_level(level: i64)

Set the log level filter.

Levels: 0=error, 1=warn, 2=info, 3=debug, 4=trace.

Examples

log.set_level(log.DEBUG);

Function get_level

pub fn get_level() -> i64

Get the current log level filter.

Function set_format

pub fn set_format(format: i64)

Set the log output format.

Use log.TEXT (0) for coloured text or log.JSON (1) for NDJSON.

Examples

log.set_format(log.JSON);
log.info_with("structured", [log.field("service", "api")]);

Function get_format

pub fn get_format() -> i64

Get the current log output format.

Function error

pub fn error(msg: string)

Log a message at error level with no structured fields.

Function error_with

pub fn error_with(msg: string, fields: Vec<string>)

Log a message at error level with structured key-value fields.

Example

log.error_with("request failed", [log.field_int("status", 500), log.field("path", "/api")]);

Function warn

pub fn warn(msg: string)

Log a message at warn level with no structured fields.

Function warn_with

pub fn warn_with(msg: string, fields: Vec<string>)

Log a message at warn level with structured key-value fields.

Function info

pub fn info(msg: string)

Log a message at info level with no structured fields.

Function info_with

pub fn info_with(msg: string, fields: Vec<string>)

Log a message at info level with structured key-value fields.

Example

log.info_with("server started", [log.field_int("port", 8080)]);

Function debug

pub fn debug(msg: string)

Log a message at debug level with no structured fields.

Function debug_with

pub fn debug_with(msg: string, fields: Vec<string>)

Log a message at debug level with structured key-value fields.

Function trace

pub fn trace(msg: string)

Log a message at trace level with no structured fields.

Function trace_with

pub fn trace_with(msg: string, fields: Vec<string>)

Log a message at trace level with structured key-value fields.

Function logger_error

pub fn logger_error(lg: Logger, msg: string, fields: Vec<string>)

Emit an error-level message through a Logger with structured fields.

Function logger_warn

pub fn logger_warn(lg: Logger, msg: string, fields: Vec<string>)

Emit a warn-level message through a Logger with structured fields.

Function logger_info

pub fn logger_info(lg: Logger, msg: string, fields: Vec<string>)

Emit an info-level message through a Logger with structured fields.

Example

let lg = log.new_logger(log.INFO, log.JSON);
log.logger_info(lg, "ready", [log.field("svc", "auth")]);

Function logger_debug

pub fn logger_debug(lg: Logger, msg: string, fields: Vec<string>)

Emit a debug-level message through a Logger with structured fields.

Function logger_trace

pub fn logger_trace(lg: Logger, msg: string, fields: Vec<string>)

Emit a trace-level message through a Logger with structured fields.

Types

Struct Logger

A logger value with its own level filter and output format.

Construct with log.new_logger(level, format). Pass to logger_* functions; it is a plain record so it can be stored in actor fields, passed to functions, or kept in a let binding.

Example

let lg = log.new_logger(log.DEBUG, log.JSON);
log.logger_info(lg, "ready", [log.field_int("port", 8080)]);

Fields

level: i64
format: i64

Constants

Constant ERROR

pub const ERROR: i64 = 0

Error-level severity (highest priority).

Constant WARN

pub const WARN: i64 = 1

Warning-level severity.

Constant INFO

pub const INFO: i64 = 2

Info-level severity (default threshold after setup()).

Constant DEBUG

pub const DEBUG: i64 = 3

Debug-level severity.

Constant TRACE

pub const TRACE: i64 = 4

Trace-level severity (lowest priority).

Constant TEXT

pub const TEXT: i64 = 0

Coloured text output format (default).

Constant JSON

pub const JSON: i64 = 1

Single-line JSON (NDJSON) output format.