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[fine] Suggestion for improvement in match

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No special keyword. Exhaustivity is harder.
This commit is contained in:
John Doty 2024-01-30 06:39:10 -08:00
parent f2e82942df
commit 93c9dcd13b
1 changed files with 22 additions and 19 deletions
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41
fine/tests/expression/alternates.fine
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@ -8,9 +8,9 @@ class Bar {
}
fun extract_value(v: Foo or Bar) -> f64 {
if match v as Foo {
if v is Foo {
v.x // Magic type binding!
} else as Bar {
} else if v is Bar {
v.y // Same magic re-binding of the variable to the new type
} // No error; exhaustivity analysis should work.
}
@ -34,7 +34,7 @@ class Monster {
fun print(x:string) {}
fun in_range(weapon: MeleeWeapon or RangedWeapon, distance: f64) {
if match weapon as w : RangedWeapon {
if weapon is w : RangedWeapon {
distance >= w.minRange and distance <= w.maxRange
} else {
distance == 1
@ -42,26 +42,29 @@ fun in_range(weapon: MeleeWeapon or RangedWeapon, distance: f64) {
}
fun attack(weapon: MeleeWeapon or RangedWeapon, monster: Monster, distance: f64) {
// This is worse but it works.
if match weapon as MeleeWeapon and distance > 1 or
match weapon as w:RangedWeapon and (distance < w.minRange or distance > w.maxRange) {
// This is worse than Bob's final version but but it works. `is` operator
// should be the same precedence as `and` and left-associative, so the
// `and` that follows the declaration in the `is` still has the variables
// from the `is` binding in scope.
if weapon is MeleeWeapon and distance > 1 or
weapon is w : RangedWeapon and (distance < w.minRange or distance > w.maxRange) {
print("You are out of range")
return
}
// Bob says he doesn't want to do flow analysis but we're doing all our
// tricks with variables and scoping here, with one *big* bit of magic which
// is...
// Bob says he doesn't want to do flow analysis and we're not, we're using
// scoping rules and associativity to make the re-bindings work.
//
// NOTE: special syntax here: `identifier` as `TypeExpression` ALMOST means
// `identifier as identifier : TypeExpression` as the shorthand for checking
// NOTE: special syntax here: `identifier` is `TypeExpression` ALMOST means
// `identifier is identifier : TypeExpression` as the shorthand for checking
// local variables. The *almost* part is that the effective type of the
// variable changes but not the binding. (Is this what we want?)
let damage = if match weapon as w: MeleeWeapon {
//
// TODO: What do we do about captured variables?
//
let damage = if weapon is w: MeleeWeapon {
roll_dice(w.damage)
} else as w: RangedWeapon {
// This is the trick here: else as re-uses the expression from the match
// and so we can do exhaustivity analysis.
} else if weapon is w: RangedWeapon {
w.maxRange - w.minRange
};
@ -75,7 +78,7 @@ fun attack(weapon: MeleeWeapon or RangedWeapon, monster: Monster, distance: f64)
}
fun more_examples(weapon: MeleeWeapon or RangedWeapon) -> f64 or () {
if match weapon as w: RangedWeapon and w.maxRange > 10 {
if weapon is w: RangedWeapon and w.maxRange > 10 {
// w is still in scope here; the `and` is bound into a predicate expression
// and breaks exhaustivity
w.minRange
@ -105,20 +108,20 @@ fun test() -> f64 {
// A single step of an iterator...
let it = new Iterator { current: 0 };
if match it.next() as v: f64 {
if it.next() is v: f64 {
sum = sum + v;
}
// Looping by hand over an iterator is pretty clean.
let it = new Iterator { current: 0 };
while match it.next() as v: f64 {
while it.next() is v: f64 {
sum = sum + v;
}
// Unroll by hand...
let it = new Iterator { current: 0 };
loop {
if match it.next() as v: f64 {
if it.next() is v: f64 {
sum = sum + v;
} else {
return sum;