Orkuncakilkaya
0d1b09e4f0
A fallible function returns a `result` value, built with ok(payload) on success
or err(message) on failure. The caller recovers a value with `try EXPR else {
… }`: on ok the whole expression is the payload; on err the else block runs —
with the failure message bound to `error` — and its trailing expression supplies
the fallback. It is a plain branch on the result's tag: no exceptions, no hidden
control flow, nothing unwinds. is_ok(r) / is_err(r) classify without unwrapping.
Payloads are any i32-width scalar (int/fixed/bool/entity). The feature is
additive and only kicks in when ok/err/try are used, so untouched programs
compile byte-identically (verified) and the C-free bootstrap fixpoint holds.
Complements panic/assert from #8 (the unrecoverable half). The optional
top-level frame `recover` stays deferred (needs a frame-abort mechanism); the
full tagged-union/any generalization is tracked in #1.
Adds the `try` keyword and ok/err/is_ok/is_err builtins across the compiler,
the vocabulary header, JetBrains + TextMate/VSCode grammars, the docs inventory
and pages, examples/library/recover.ludic, and a regression case.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
28 lines
1.2 KiB
Markdown
28 lines
1.2 KiB
Markdown
---
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id: fn-err
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name: err
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category: builtins
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kind: builtin
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tokens: err
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sig: err(msg: string) -> result
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tip: Wrap a failure message in a result — the sad half, recovered by try/else.
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order: 13
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---
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Wraps a failure in a <code>result</code>, carrying a message that says what went wrong. It is the counterpart to <a href="fn-ok"><code>ok</code></a>: a fallible function (declared <code>-> result</code>) returns <code>err("…")</code> on the sad path instead of crashing or returning a magic sentinel. The caller recovers with <a href="kw-try"><code>try</code></a>/<code>else</code> — the <code>else</code> block sees the message as <code>error</code> — or tests it with <a href="fn-is_err"><code>is_err</code></a>. Unlike <a href="fn-panic"><code>panic</code></a>, which aborts, <code>err</code> is a value: the program keeps running and chooses a fallback.
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Parameters:
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- `msg` — a message describing the failure (a string)
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```ludic
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program Config {
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function volume(pct: int) -> result {
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if pct < 0 or pct > 100 { return err("volume out of range") }
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return ok(pct)
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}
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test "err drives the fallback" {
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let v = try volume(150) else { 100 } # clamp to a safe default
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expect_eq(v, 100)
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}
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}
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```
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