Sometimes I wish for custom *binding* patterns in Swift. Is something
like this already in the works? Anyone else wishing for this?
I have attached some code where I fake it, but these examples
show what I'm really after:
/* Match complex numbers, let expressions with type qualification: */
for elt in [1.0 + î, 2.0 + 3.0 * î, 4.0 + 5.0 * î, 6.0 * î] {
switch elt {
case î * (let d: Double):
print("matched î * \(d)")
case 1 + î * (let a: Double):
print("matched 1 + î * \(a)")
case (let b: Double) + î * (let c: Double):
print("matched \(b) + î * \(c)")
default:
print("no match")
}
}
/* Match complex numbers, let expressions with types inferred: */
for elt in [1.0 + î, 2.0 + 3.0 * î, 4.0 + 5.0 * î, 6.0 * î] {
switch elt {
case î * (let d):
print("matched î * \(d)")
case 1 + î * (let a):
print("matched 1 + î * \(a)")
case (let b) + î * (let c):
print("matched \(b) + î * \(c)")
default:
print("no match")
}
}
/* Match strings, assigning substrings to numeric types a la scanf(3): */
if case "\(let a: Double) + \(let b: Double) î" = "1 + 2 î" {
print("matched \(a) + \(b) î")
}
/* Approximately match strings; `fuzz` is an "edit distance" between
* the pattern and the match.
*/
if case ApproximateMatch("\(let a: Double) + \(let b: Double) î", let fuzz) = "1 + 2 * î", fuzz < 5 {
print("matched \(a) + \(b) î with fuzz \(d)")
}
/* Simplify an algebraic expression: n1 / d + n2 / d -> (n1 + n2) / d.
binding.swift (496 Bytes)
complex.swift (1.42 KB)
double.swift (1.39 KB)
main.swift (636 Bytes)
···
*
* Original source:
*/
if case .sum(.quotient(let ln, let ld),
.quotient(let rn, let rd)) = expr, ld == rd {
return evaluate(.quotient(.sum(ln, rn), ld), env)
}
/* => with operator overloading (no custom binding patterns) becomes: */
if case .sum(.quotient(let ln, let ld),
.quotient(let rn, let rd)) = expr, ld == rd {
return evaluate((ln + rn) / ld, env)
}
/* => with custom binding patterns and operator overloading becomes: */
if case (let ln: Expr) / (let ld: Expr) +
(let rn: Expr) / (let rd: Expr) = expr, ld == rd {
return evaluate((ln + rn) / ld, env)
}
/* => with type inference becomes: */
if case (let ln) / (let ld) + (let rn) / (let rd) = expr, ld == rd {
return evaluate((ln + rn) / ld, env)
}
Dave
--
David Young
dyoung@pobox.com Urbana, IL (217) 721-9981
