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RohansiRohansi
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Switch expressions
1 parent 3abde5d commit ca93e43

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Lines changed: 1091 additions & 162 deletions

‎Mond.Tests/Expressions/SwitchExpressionTests.cs‎

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using NUnit.Framework;
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namespace Mond.Tests.Expressions
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{
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[TestFixture]
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public class SwitchExpressionTests
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{
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[Test]
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public void JumpTableArms()
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{
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var result = Script.Run(@"
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fun describe(x) {
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return x switch {
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1 -> 'one',
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2 -> 'two',
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3 -> 'three',
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4 -> 'four',
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_ -> 'many'
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};
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}
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return describe(1) + describe(3) + describe(9);
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");
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Assert.That(result, Is.EqualTo((MondValue)"onethreemany"));
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}
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[Test]
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public void MultipleValuesPerArm()
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{
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var result = Script.Run(@"
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fun describe(x) {
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return x switch {
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'a', 'b' -> 1,
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'c' -> 2,
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_ -> 3
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};
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}
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return [describe('a'), describe('b'), describe('c'), describe('d')];
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");
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Assert.That(result[0], Is.EqualTo((MondValue)1));
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Assert.That(result[1], Is.EqualTo((MondValue)1));
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Assert.That(result[2], Is.EqualTo((MondValue)2));
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Assert.That(result[3], Is.EqualTo((MondValue)3));
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}
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[Test]
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public void NonConstantArms()
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{
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var result = Script.Run(@"
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const a = 10;
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var b = 20;
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fun describe(x) {
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return x switch {
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a -> 'a',
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b -> 'b',
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_ -> 'other'
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};
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}
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return describe(10) + describe(20) + describe(30);
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");
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Assert.That(result, Is.EqualTo((MondValue)"abother"));
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}
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[Test]
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public void TrailingComma()
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{
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var result = Script.Run(@"
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return 1 switch {
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1 -> 'one',
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_ -> 'other',
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};
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");
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Assert.That(result, Is.EqualTo((MondValue)"one"));
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}
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[Test]
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public void BindingArmWithGuard()
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{
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var result = Script.Run(@"
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fun describe(x) {
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return x switch {
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var n when n > 100 -> 'big',
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var n when n > 10 -> 'medium',
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_ -> 'small'
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};
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}
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return describe(500) + describe(50) + describe(5);
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");
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Assert.That(result, Is.EqualTo((MondValue)"bigmediumsmall"));
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}
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[Test]
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public void ValueArmWithGuard()
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{
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var result = Script.Run(@"
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var flag = false;
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fun describe(x) {
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return x switch {
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1 when flag -> 'flagged',
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1 -> 'one',
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_ -> 'other'
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};
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}
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var a = describe(1);
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flag = true;
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return a + describe(1);
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");
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Assert.That(result, Is.EqualTo((MondValue)"oneflagged"));
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}
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[Test]
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public void ObjectDestructuringArm()
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{
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var result = Script.Run(@"
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fun describe(x) {
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return x switch {
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{ name, age } -> name + ' is ' + age,
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{ name } -> name,
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_ -> 'unknown'
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};
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}
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return [
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describe({ name: 'bob', age: 5 }),
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describe({ name: 'joe' }),
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describe(123)
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];
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");
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Assert.That(result[0], Is.EqualTo((MondValue)"bob is 5"));
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Assert.That(result[1], Is.EqualTo((MondValue)"joe"));
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Assert.That(result[2], Is.EqualTo((MondValue)"unknown"));
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}
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[Test]
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public void ObjectDestructuringAlias()
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{
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var result = Script.Run(@"
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return { name: 'bob' } switch {
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{ name: n } -> n,
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_ -> 'unknown'
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};
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");
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Assert.That(result, Is.EqualTo((MondValue)"bob"));
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}
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[Test]
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public void ArrayDestructuringArm()
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{
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var result = Script.Run(@"
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fun describe(x) {
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return x switch {
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[a, b] -> a + b,
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[a, ...rest] -> a + rest.length(),
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_ -> -1
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};
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}
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return [describe([1, 2]), describe([1, 2, 3]), describe('nope')];
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");
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Assert.That(result[0], Is.EqualTo((MondValue)3));
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Assert.That(result[1], Is.EqualTo((MondValue)3));
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Assert.That(result[2], Is.EqualTo((MondValue)(-1)));
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}
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[Test]
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public void ArmScopesAreIsolated()
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{
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Assert.Throws<MondCompilerException>(() => Script.Run(@"
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var x = { a: 1 } switch {
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{ a } -> a,
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_ -> 0
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};
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return a;
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"));
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}
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[Test]
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public void NestedInExpressions()
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{
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var result = Script.Run(@"
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fun add(a, b) -> a + b;
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var x = 1;
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return add(x switch { 1 -> 10, _ -> 0 }, x == 1 ? x switch { 1 -> 5, _ -> 0 } : 0);
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");
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Assert.That(result, Is.EqualTo((MondValue)15));
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}
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[Test]
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public void NestedSwitchExpression()
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{
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var result = Script.Run(@"
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return 1 switch {
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1 -> 2 switch {
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2 -> 'nested',
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_ -> 'no'
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},
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_ -> 'no'
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};
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");
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Assert.That(result, Is.EqualTo((MondValue)"nested"));
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}
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[Test]
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public void SubjectEvaluatedOnce()
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{
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var result = Script.Run(@"
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var calls = 0;
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fun next() {
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calls++;
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return 3;
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}
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var value = next() switch {
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1 -> 'one',
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3 -> 'three',
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_ -> 'other'
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};
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return value + calls;
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");
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Assert.That(result, Is.EqualTo((MondValue)"three1"));
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}
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[Test]
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public void SwitchStatementStillWorks()
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{
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var result = Script.Run(@"
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var x = 2;
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switch (x) {
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case 1:
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return 'one';
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case 2:
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return 'two';
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default:
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return 'other';
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}
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");
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Assert.That(result, Is.EqualTo((MondValue)"two"));
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}
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[Test]
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public void MissingDiscardArm()
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{
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Assert.Throws<MondCompilerException>(() => Script.Run(@"
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return 1 switch {
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1 -> 'one'
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};
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"));
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}
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[Test]
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public void ArmAfterDiscardArm()
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{
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Assert.Throws<MondCompilerException>(() => Script.Run(@"
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return 1 switch {
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_ -> 'other',
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1 -> 'one'
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};
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"));
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}
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[Test]
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public void DiscardArmCantHaveGuard()
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{
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Assert.Throws<MondCompilerException>(() => Script.Run(@"
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return 1 switch {
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_ when true -> 'other'
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};
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"));
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}
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[Test]
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public void DuplicateConstantArms()
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{
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Assert.Throws<MondCompilerException>(() => Script.Run(@"
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return 1 switch {
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1 -> 'one',
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1 -> 'uno',
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_ -> 'other'
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};
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"));
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}
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}
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}

‎Mond/Compiler/CompilerError.cs‎

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -32,6 +32,10 @@ static class CompilerError
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public const string DuplicateCase = "Duplicate case value";
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public const string DuplicateDefault = "Cannot have more than one default case";
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public const string SwitchExprMissingDiscard = "Switch expressions must end with a '_' arm";
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public const string SwitchExprArmAfterDiscard = "Switch expression arms cannot appear after the '_' arm";
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public const string SwitchExprDiscardGuard = "The '_' arm of a switch expression cannot have a 'when' guard";
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public const string ExportMustBeFollowedByKeywords = "'export' modifier can only be applied to 'const', 'fun', or 'seq' declarations";
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public const string ExportMustBeFollowedByDeclaration = "'export' modifier can only be applied to declaration expressions";
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public const string ExportMustBeFollowedByNonEmptyDeclaration = "'export' modifier cannot be applied to expressions with no declarations";

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