Documentation for Deptle Terminal.

Every DSL compile error is printed in a consistent, structured format: a headline with an error code, a pointer at the offending source location, a snippet with a caret under the exact tokens, and optional help: or note: lines.

• **Headline** — error[EXXXX]: <message>. The code (e.g. E0521) is stable and can be grepped.
• **Location** — --> <file>:<line>:<col> points at the start of the primary span.
• **Snippet** — the source line with a caret (^) under the exact tokens that caused the error. When a span crosses multiple lines, the snippet shows the opening line, an elided ..., and the closing line. Very long lines are windowed around the span (prefixed/suffixed with ...) so the interesting tokens stay visible.
• **Context line** — when the error doesn't start on line 1 the compiler also prints the preceding source line above the primary, to give the reader a little surrounding code.
• **Secondary label** — for errors that reference two locations (e.g. a duplicate Parameter name), a second caret is printed at the first occurrence with previously declared here.
• **Help / Note** — lines prefixed with note: explain *why* something is wrong; lines prefixed with help: suggest a concrete fix. note: lines are printed first, help: second. Multi-line notes are indented under the first character of the message so they read as a coherent paragraph.
• **Did you mean?** — when an identifier is unknown the compiler tries to find the closest in-scope name via edit distance and suggests it in a help: line.

1error[E0521]: `Parameter n` is missing `min`
2  --> <strategy.py>:3:14
3   |
4 3 |     n: int = Parameter(default=5, max=10)
5   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
6   |
7   = help: pass `min=...` (the lower bound for optimization sweeps)

Errors raised while analyzing class fields, Parameter/State/Extra declarations, and asset config.

• E0500 — on_tick has the wrong signature. Use (self, tick) or (self, tick, sys).
• E0501 — on_bar is no longer supported; rename it to on_tick and configure bars in the UI.
• E0502 — missing required on_tick method on the strategy class.
• E0504 — a field name uses the reserved deptle_bar_ prefix.
• E0505 — duplicate field name across Parameter / State / Extra.
• E0510–E0512 — bar_timeframe / bar_fill_mode / required_assets / asset_slots annotation is wrong.
• E0520–E0525 — Parameter(...) is missing default / min / max, or has min > max, default out of range, or non-positive step.
• E0530–E0540 — State(...) indicator / array / size issues.
• E0550–E0554 — Extra(...) positional args, bad annotation, missing / out-of-range binding.
• E0570–E0577 — required_assets / asset_slots validation.

Errors raised while lowering the body of on_tick into the internal IR.

• E02xx — statement-level issues (unsupported for/while, disallowed assignment target, augassign type mismatches, unsupported return shape).
• E03xx — expression-level issues (unknown name, unsupported attribute access, bad literal form, slice / subscript errors).
• E04xx — call / ordering issues (unknown builtin, wrong arg count, bad Order.*(...) shape, disallowed call target).

How to quickly resolve compile errors.

• Fix errors top-to-bottom: the compiler stops at the first hard error in declarations before lowering the body.
• Error codes are stable across releases — pin them in team runbooks or tests.
• If a help: line suggests a different keyword (e.g. size= instead of positional), prefer that wording verbatim.
• Parse errors (syntax) are reported separately by the editor before the DSL compiler runs.