⚙️ Mold Defaults

A mold script can embed default CLI options via # fimod: comment directives. This makes scripts self-describing — callers don't need to remember which format or options a script expects.

Where to put directives

Directives must appear at the very top of the file, before any code.

# fimod: input-format=csv, output-format=json
# fimod: csv-delimiter=;
def transform(data, args, env, headers):
    return [{"name": row["name"], "age": int(row["age"])} for row in data]

Running this with just fimod s -i data.csv -m script.py automatically uses ; as the delimiter.

📋 Supported directives

Directive	Type	Description
`input-format=<fmt>`	value	Input format (`json`, `ndjson`, `yaml`, `toml`, `csv`, `txt`, `lines`)
`output-format=<fmt>`	value	Output format
`csv-delimiter=<char>`	value	CSV input delimiter character
`csv-output-delimiter=<char>`	value	CSV output delimiter character
`csv-header=<cols>`	value	Explicit column names (comma-separated)
`csv-no-input-header`	flag	Input has no header row
`csv-no-output-header`	flag	Don't write header in output
`no-follow`	flag	Don't follow HTTP redirects
`arg=<name> [desc]`	value	Document an `--arg` parameter (name + optional description)
`env=<VAR> [desc]`	value	Document an `--env` variable (name + optional description)

📏 Priority and parsing rules

CLI wins by default

Explicit CLI arguments always override mold defaults declared with =.

Directives are read from the top of the file — scanning stops at the first non-comment, non-blank line
Multiple key-value pairs can appear on the same # fimod: line, comma-separated
Unknown keys are silently ignored
Directives in -e inline expressions are never parsed

🔒 Forced directives (`!=`)

Use != instead of = to declare a directive as forced — the CLI cannot override it.

# fimod: output-format!=yaml
def transform(data, **_):
    return data

# The mold forces YAML regardless of what the caller passes
fimod s -i data.json -m strict.py --output-format json
# → output is YAML, not JSON

This is useful for molds that produce a format incompatible with others (e.g., a mold that always emits YAML for a downstream tool).

Debug info

Run with --debug to see which directives are forced:

[debug] mold forces output-format=yaml

Forced and default directives can be mixed on the same mold:

# fimod: input-format!=csv, output-format=json

Here input-format is locked to csv; output-format is a suggestion that the CLI can override.

💡 Complete example

# fimod: input-format!=csv
# fimod: output-format=json
# fimod: csv-delimiter=;
# fimod: csv-no-input-header
def transform(data, args, env, headers):
    # data = [{"col0": ..., "col1": ...}, ...]
    return [{"name": row["col0"], "value": int(row["col1"])} for row in data]

# ✅ Use defaults — input-format is locked to csv
fimod s -i data.csv -m script.py

# 🔀 Override output format at call time (allowed — it's a default, not forced)
fimod s -i data.csv -m script.py --output-format yaml

# ⚠️  --input-format is ignored — the mold forces csv
fimod s -i data.csv -m script.py --input-format json