# `mix tptp.gen`
[🔗](https://github.com/jcschuster/tptp/blob/v0.1.3/lib/mix/tasks/tptp.gen.ex#L1)

Regenerates the committed sources from the two vendored TPTP World BNFs,
`priv/bnf/SyntaxBNF-v*` and `priv/bnf/SZSOntology.bnf`.

This is a maintainer action, taken when a new TPTP release changes the BNF. The
generated `.yrl` is committed, so an installing user needs nothing but OTP —
`yecc` ships with it and Mix compiles `src/*.yrl` automatically.

Five files are generated. From the `SyntaxBNF`: `src/tptp_parser.yrl`,
`lib/tptp/printer/shapes.ex` and `test/support/bnf_oracle.ex`. From
`SZSOntology.bnf`: `lib/tptp/szs/ontology.ex`. From both:
`lib/tptp/bnf/vocabulary.ex`, whose `<status_value>` list the `SyntaxBNF`
references and the SZS BNF defines.

    mix tptp.gen
    mix tptp.gen --check

`--check` regenerates into memory and fails if the result differs from the
committed output, which is what prevents a generated file from being hand-edited.

The task prints the departures made from a mechanical translation. That list comes
from `Tptp.Bnf.Generator.departures/0`, which renders it from the constants
producing it, so a release requiring a further departure is reported rather than
absorbed into the grammar.

## Recovering from an uncompilable grammar

Mix runs the `:yecc` compiler before `:elixir`, so a `src/tptp_parser.yrl` that
does not compile prevents the task that would rewrite it from running. A manual
edit or an incomplete merge therefore renders the generator unreachable through
its own output.

Delete the file and run the task again. With no `.yrl` present there is nothing
for yecc to compile, `Tptp.Parser`'s calls into `:tptp_parser` produce only an
undefined-module warning, and the task regenerates all four outputs from the
vendored BNF. The generated grammar is a function of the BNF alone, so
discarding it loses nothing.

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*Consult [api-reference.md](api-reference.md) for complete listing*