On Tue, 8 May 2007, Ralf Hemmecke wrote:
[...]
| > Spad needs to move to mutual recursion (with appropriate restrictions)
| > anyway.
|
| Does someone know of an instance of mutual recursion in the Axiom library that
| cannot be cured with "extend"? (I am not saying that I don't want mutual
| recursion, but rather whether it is needed for the current Axiom library.)
This is not from the Axiom library, but I do run into it very often.
Assume I want to represent a typed abstract syntax tree for the
C language. In C, I have the following (simplifying a bit)
* literals
* declarations
* types
* expressions
* ...
A type can be:
- an identifier
- a structure, with components that are are fields (declarations
involving names, types, and expressions)
- an array, with components that are a type and an expression
- ...
An expression among other things, contains:
- sizeof (type)
I want distinct domains for literals, fields, types, expressions, etc.
In Haskell (or Boot), I could write:
type Symbol = String
data Type = Identifier Symbol
| Structure (Maybe Symbol) [Field]
| Array Type Expression
-- and more
data Field = Bitfield (Maybe Symbol) Expression Type
| NonBitfield Symbol Type
data Expression = StringLiteral String
| SizeofExpr Expression
| SizeofType Type
-- and more
What would be a "natural" and concise expression of that in Spad?
-- Gaby
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