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Syntax for term re-writing:
(rule <pattern>
<substitute>)
Pattern examples:
(? a)
(? a number?)
(? a not-number?)
(? a number? odd?)
(? a (free? x))
(? a (neq? 0))
; match zero or more into a list; expand list in-line, same order
(?* l)
Full examples:
(rule (/ 1 (/ (? a) (? b)))
(/ (? b) (? a)))
Simplifications:
- variable names must be single Latin letter
- predicates are fixed to a set of type checks
## Implementation
Separate rule lists, one for each "head" type (Sum, Product, Power, etc).
struct RuleSet {
sum_rules: Vec<Rule>,
product_rules: Vec<Rule>,
[...]
}
struct Rule {
variables: HashMap<type, char, Vec<predicates>>,
pattern: MatchExpr,
substitute: MatchExpr,
}
enum MatchExpr {
variable: char,
atom: CExpr,
list: { head: expr_type, tail: Vec<MatchExpr> },
}
----------------
Backburner:
- are additional pattern-wide predicates necessary or helpful?
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