Andrew Hunter wrote:
Several times now I've had to define an EDSL for working with
(vaguely) numeric expressions. For stuff like 2*X+Y, this is easy,
looking pretty much like:
data Expr = Const Integer | Plus Expr Expr | Times Expr Expr
instance Num Expr where
fromInterger = Const
(+) = Plus
(*) = Times
>
Does anyone know of a good solution, here? Are there good
substitutions for all the six operators that are important
(<,>,>=,<=,==,/=), that are close enough to be pretty-looking but not
used for other important modules?
If you're just wanting to build Exprs, then the canonical solution is to
use ':' as in (:>), (:>=), (:==), (:/=), (:<=), (:<). The colon is
considered a "capital symbol" and so it's what you use as the first
letter of symbolic constructors. For symmetry, many folks will ad
another colon at the end as well.
> data Expr = Const Integer | Expr :+: Expr | Expr :*: Expr | Expr
:>: Expr | ...
--
Live well,
~wren
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