DSL

DSL = Domain Specific Language

EDSL = Embedded Domain Specific Language

While a DSL has its own compiler/interpreter, an EDSL is embedded within another language. Thus the EDSL uses the a subset of the syntax of the host language.

Shallow Embedding

Shallow embedding is when the EDSL reuses the semantics of the host language.

type Exp = Int

plus  :: Exp -> Exp -> Exp
times :: Exp -> Exp -> Exp
const :: Int        -> Exp

The example above defines an EDSL for doing math in Haskell and reuses Haskells semantics of Integer for this.

Deep Embedding

Deep embedding is when defining a data type and forming an AST through the data type. The syntax and semantics are separated.

data Exp
    = Const Int
    | Add Exp Exp
    | Mul Exp Exp
    | Div Exp Exp

sEval :: Exp -> Int
Eval e = case e of
    Const x -> x
    Add e1 e2 -> sEval e1 + sEval e2
    Mul e1 e2 -> sEval e1 * sEval e2
    Div e1 e2 -> sEval e1 `div ` sEval e2