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I found this code on the front page of the Yesod project:
import Yesod
data HelloWorld = HelloWorld
mkYesod "HelloWorld" [$parseRoutes|/ Home GET|]
instance Yesod HelloWorld where approot _ = ""
getHome = applyLayout [$hamlet|%h1 Hello World|]
main = toWaiApp HelloWorld >>= basicHandler 3000
What language features are used in [$parseRoutes|/ Home GET|] and [$hamlet|%h1 Hello World|] to get the $, |, / and % symbols working, and what do the symbols do?
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asked Jul 19 '10 23:07
() is very often used as the result of something that has no interesting result. For example, an IO action that is supposed to perform some I/O and terminate without producing a result will typically have type IO () .
Overview. We use pattern matching in Haskell to simplify our codes by identifying specific types of expression. We can also use if-else as an alternative to pattern matching. Pattern matching can also be seen as a kind of dynamic polymorphism where, based on the parameter list, different methods can be executed.
Haskell uses a traditional Hindley-Milner polymorphic type system to provide a static type semantics [4, 6], but the type system has been extended with type classes (or just classes) that provide a structured way to introduce overloaded functions. A class declaration (Section 4.3.
Haskell (/ˈhæskəl/) is a general-purpose, statically-typed, purely functional programming language with type inference and lazy evaluation.
Those would be a Quasiquotation. It's a way to use Template Haskell to embed another language into Haskell. The quasiquotes 'parseRoutes and hamlet define how to parse and interpret what is inside the bracket [$FOO| ... ]. Many more details at the link above.
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