Formatting Output
A formatter turns an event into text. Sinks take one as an option.
| Formatter | Module | Output |
|---|---|---|
| Output templates | Formatting.Text.template |
{Timestamp}, {UtcTimestamp}, {Level}, {Message}, {Exception}, {Properties}, {NewLine}, {TraceId}, {SpanId}, and any property such as {SourceContext}
|
| JSON | Formatting.Json.formatter |
one object with properties and renderings; renderMessage and closingDelimiter options |
| Compact JSON |
Formatting.Compact.compact, rendered
|
newline-delimited objects with @t, @mt or @m, @r, @l, @x, @tr, @sp
|
| Expression templates | Expressions.template |
holes of expressions and #if, #else if, #else, #each, #delimit, #end
|
Level formats: u3 gives WRN, w3 gives wrn, t4 gives Warn. Message:l writes text without quotes and Message:j writes structures as JSON. Formatting.Reader reads compact JSON back into events with readLine, readAll, and readFile.
module Ex06Formatting
import Std.Io as Io
import Std.Option as Option
import PuduLangLog.Event as Event
import PuduLangLog.Expressions as Expressions
import PuduLangLog.Failure as Failure
import PuduLangLog.Formatting.Compact as Compact
import PuduLangLog.Formatting.Json as Json
import PuduLangLog.Formatting.Reader as Reader
import PuduLangLog.Formatting.Text as Text
import PuduLangLog as Log
import PuduLangLog.Value as Value
export fn main() -> Int {
let base = Event.create(Log.Timestamp{millis: 1790604309123, offset: 120}, Log.Warning, "Disk \{Disk\} is \{Percent:0.0\}% full", [
Value.property("Disk", Value.text("C")),
Value.property("Percent", Value.decimal(93.25d)),
Value.property("SourceContext", Value.text("Ops.Disks"))
])
let event = Event.withFailure(&base, Failure.of("IoError", "no space left"))
let text = Text.template("\{Timestamp:yyyy-MM-dd HH:mm:ss zzz\} [\{Level:u3\}] \{SourceContext\}: \{Message:lj\} \{Properties:j\}\{NewLine\}\{Exception\}")
let _a = Io.writeLine(text(&event))
let _b = Io.writeLine(Json.formatter(Json.Options{renderMessage: true, closingDelimiter: ""})(&event))
let compact = Compact.compact()(&event)
let _c = Io.writeLine(compact.trim())
let _d = Io.writeLine(Compact.rendered()(&event).trim())
let layout = match Expressions.template("\{@l:u3\} \{#if SourceContext is not null\}(\{SourceContext\}) \{#end\}\{@m\}\{#if @x is not null\} !! \{@x\}\{#end\}") {
case Ok(formatter) => formatter
case Err(problem) => panic(problem)
}
let _e = Io.writeLine(layout(&event))
match Reader.readLine(compact) {
case Ok(read) => { let _f = Io.writeLine("read back: " + show(read.level) + " " + Event.message(&read) + " / " + show(Option.map(read.failure, |problem: Log.Failure| problem.kind))) }
case Err(problem) => { let _g = Io.writeErrorLine(problem) }
}
0
}
Check it and run it:
pudu check src/Ex06Formatting.pudu
pudu run src/Ex06Formatting.puduOutput:
2026-09-28 16:05:09 +02:00 [WRN] Ops.Disks: Disk C is 93.3% full {}
IoError: no space left
{"Timestamp":"2026-09-28T16:05:09.1230000+02:00","Level":"Warning","MessageTemplate":"Disk {Disk} is {Percent:0.0}% full","RenderedMessage":"Disk \"C\" is 93.3% full","Exception":"IoError: no space left","Properties":{"Disk":"C","Percent":93.25,"SourceContext":"Ops.Disks"},"Renderings":{"Percent":[{"Format":"0.0","Rendering":"93.3"}]}}
{"@t":"2026-09-28T14:05:09.1230000Z","@mt":"Disk {Disk} is {Percent:0.0}% full","@r":["93.3"],"@l":"Warning","@x":"IoError: no space left","Disk":"C","Percent":93.25,"SourceContext":"Ops.Disks"}
{"@t":"2026-09-28T14:05:09.1230000Z","@m":"Disk \"C\" is 93.3% full","@i":"c9fb6c7e","@l":"Warning","@x":"IoError: no space left","Disk":"C","Percent":93.25,"SourceContext":"Ops.Disks"}
WRN (Ops.Disks) Disk C is 93.3% full !! IoError: no space left
read back: Warning Disk "C" is 93.3% full / Some("IoError")
{Properties} lists only the properties neither the message nor the output template names.