Language.Nanopass

Nanopass consists essentially of creating languages and defining passes. Languages can be created from scratch or by derivation using deflang. The tedious parts of a compiler pass (or at least, most passes) can be generated with defpass.

More details and examples are given in the readme.

Documentation

deflang :: QuasiQuoter

Define a language, either from scratch or by derivation from an existing language. The syntax is based on s-expressions.

TODO document the syntax here, or for now you can look in Nanopass.Internal.Parser More details and examples are given in the readme.

defpass :: QuasiQuoter

Define automatic translation between two langauges. This creates an Xlate type and the descend<Syntactic Category> family of functions, as well as pure variants (XlateI and descend<Syntactic Category>I) and a lifting function idXlate. A translation function is generated for each syntactic category with the same name in both source and target languages. At the moment, there is no provision for altering the name of the type or translation function(s), but I expect you'll only want to define one translation per module.

The Xlate type takes all the parameters from both languages (de-duplicating parameters of the same name), as well as an additional type parameter, which is the functor f under which the translation occurs.

The type of a descend<Syntactic Category> function is Xlate f → σ → f σ'.

If a production in the source language has subterms τ₁ … τₙ and is part of the syntactic category σ, then a hole member is a function of type τ₁ → … τₙ → f σ', where σ' is the corresponding syntactic category in the target language. Essentially, you get access all the subterms, and can use the Applicative to generate a target term as long as you don't cross syntactic categories.

If a source language has syntactic category σ with the same name as the target's syntactic category σ', then an override member is a function of type σ → Maybe (f σ'). If an override returns Nothing, then the automatic translation will be used, otherwise the automatic translation is ignored in favor of the result under the Just.

The pure variants have the same form as the Applicative ones, but:

• XlateI is not parameterized by f, nor are the types of its members,
• the members of XlateI are suffixed with the letter I, and
• the types of the descend<Syntactic Category>I functions are not parameterzed by f.

The idXlate function is used by Nanopass to translate XlateI values into Xlate values. This is done so that the same code paths can be used for both pure and Applicative translations. Under the hood, this is done with appropriate wrapping/unwrapping of Identity, which is a no-op.

None of the functions defined by this quasiquoter need to be expoted for Nanopass to function. I expect you will not export any of these definitions directly, but instead wrap them into a complete pass, and only export that pass.

More details and examples are given in the readme.

TODO document the syntax here, but for now, see parsePass for a grammar.