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Wonder how much of bidirectional type checking can be done in that manner...

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· Apr 18, 2020

For FP nerds, parsing an AST from a string is an unfold for the AST data type, type checking and generating code from the AST is a fold, and if you do fold/unfold fusion you have a one-pass compiler.

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Brendan Zabarauskas

@brendanzab

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@ArmyOfBruce

Reminds me of twitter.com/glaebhoerl/sta - I'm thinking of making a core language like this.

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@glaebhoerl

· Feb 22, 2020

If you have an LL(k) grammar, require all names to be declared prior to their use, and have a sensible type system that can be typechecked in one pass, I think you could get through the whole front end of the compiler without ever materializing an AST in memory?

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9:58 AM · Apr 20, 2020Twitter Web App

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and

I think this is essentially "finally tagless": instead of defining your structures (AST or IR) as data, define them as classes; in the parser resp. elaborator, "construct" the AST resp. IR by calling methods; make instances do elaboration, resp. perhaps code generation, directly.

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@glaebhoerl

Apr 20, 2020

You can also define instances to construct an actual AST/IR as data, if you need that, for example to do analysis/optimization. (I'm not sure if you couldn't also do those as a directly fused chain, but I'm pretty sure you couldn't if you need to compute fixed points.)

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