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📝 the abstract parsers.

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Rob Rix 2019-10-02 15:05:33 -04:00
parent 17481f566e
commit 80fbd7184f
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src/Parsing/Parser.hs
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@ -21,6 +21,8 @@ module Parsing.Parser
, phpASTParser
, haskellParser
-- * Abstract parsers
-- $abstract
, SomeParser(..)
, goParser'
, haskellParser'
@ -201,6 +203,31 @@ someASTParser Markdown = Nothing
someASTParser Unknown = Nothing
-- $abstract
-- Most of our features are intended to operate over multiple languages, each represented by disjoint term types. Thus, we typically implement them using typeclasses, allowing us to share a single interface to invoke the feature, while specializing the implementation(s) as appropriate for each distinct term type.
--
-- In order to accomplish this, we employ 'SomeParser', which abstracts over parsers of various term types, while ensuring that some desired constraint holds. Constructing a @'SomeParser' c@ requires satisfiyng the constraint @c@ against the underlying 'Parser'’s term type, and so it can be used to parse with any of a map of parsers whose terms support @c@.
--
-- In practice, this means using 'Control.Effect.Parse.parseWith', and passing in a map of parsers to select from for your feature. It is recommended to define the map as a concrete top-level binding using the abstract parsers or ideally the canonical maps of parsers, below; using the abstracted parsers or canonical maps directly with 'Control.Effect.Parse.parseWith' will lead to significantly slower compiles.
--
-- Bad:
--
-- @
-- isFancy :: (Carrier sig m, Member Parse sig) => Blob -> m Bool
-- isFancy = parseWith (preciseParsers @Fancy) (pure . isTermFancy) -- slow compiles!
-- @
--
-- Good:
--
-- @
-- fancyParsers :: 'Map' 'Language' ('SomeParser' Fancy 'Loc')
-- fancyParsers = preciseParsers
--
-- isFancy :: (Carrier sig m, Member Parse sig) => Blob -> m Bool
-- isFancy = parseWith fancyParsers (pure . isTermFancy) -- much faster compiles
-- @
-- | A parser producing terms of existentially-quantified type under some constraint @c@.
--
-- This can be used to perform actions on terms supporting some feature abstracted using a typeclass, without knowing (or caring) what the specific term types are.