Lesson plan
Template Haskell
Template Haskell (Template Meta-Haskell for early versions) is an experimental language extension to the functional programming language Haskell, implemented in the Glasgow Haskell Compiler (GHC) version 6 and later. It allows compile time metaprogramming and generative programming by means of manipulating abstract syntax trees and 'splicing' results back into a program. The abstract syntax is represented using ordinary Haskell data types and the manipulations are performed using ordinary Haskell functions. 'Quasi-quote' brackets [| and |] are used to get the abstract syntax tree for the enclosed expression and 'splice' brackets $( and ) are used to convert from abstract syntax tree into code. As of GHC-6.10, Template Haskell provides support for user-defined quasi-quoters, which allows users to write parsers which can generate Haskell code from an arbitrary syntax. This syntax is also enforced at compile time. For example, using a custom quasi-quoter for regular expressions could look like this: digitsFollowedByLetters = [$re| \d+ \s+ |]
Article summary
Template Haskell (Template Meta-Haskell for early versions) is an experimental language extension to the functional programming language Haskell, implemented in the Glasgow Haskell Compiler (GHC) version 6 and later. It allows compile time metaprogramming and generative programming by means of manipulating abstract syntax trees and 'splicing' results back into a program. The abstract syntax is represented using ordinary Haskell data types and the manipulations are performed using ordinary Haskell functions. 'Quasi-quote' brackets [| and |] are used to get the abstract syntax tree for the enclosed expression and 'splice' brackets $( and ) are used to convert from abstract syntax tree into code. As of GHC-6.10, Template Haskell provides support for user-defined quasi-quoters, which allows users to write parsers which can generate Haskell code from an arbitrary syntax. This syntax is also enforced at compile time. For example, using a custom quasi-quoter for regular expressions could look like this: digitsFollowedByLetters = [$re| \d+ \s+ |]
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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