Table of Contents

Control flow

Raven is expression-oriented, but it also supports statement-form control flow for running code in order, repeating work, and leaving a block early.

Expression and statement context

Every occurrence of code appears in either an expression context or a statement context.

Concept

  • An expression context expects a value.
  • A statement context expects an action rather than a value.
  • Expressions are valid in statement context; their values are discarded unless captured.
  • Some constructs are statement-only because they do not yield a value.

Example

val value = if flag { 1 } else { 2 }

if flag {
    Log("side effect")
}

Rules

  • Expression contexts include assignment right-hand sides, invocation arguments, match scrutinees and arms, if expression branches, and the final position of a block expression.
  • Statement contexts include block bodies before the final expression, method bodies, accessor bodies, and any location terminated by a newline or semicolon.
  • Statement-form return, yield return, yield break, break, continue, statement-form throw, and statement-form try are valid only in statement context.
  • Statements are terminated by a newline, an optional semicolon, }, or a construct-closing keyword such as else, catch, or finally.
  • Newlines inside parentheses, brackets, or braces do not terminate statements.
  • End-of-file fulfills the same terminating role as a newline.

When extra tokens remain on the same line after a statement has already completed, the parser reports RAV1019: Expected newline or ';' to terminate the statement.【F:src/Raven.CodeAnalysis/DiagnosticDescriptors.xml†L256-L262】 Insert semicolons to separate statements intentionally written on one line or move the remaining tokens to the following line.

System.Console.WriteLine("Examples") 42 // RAV1019
System.Console.WriteLine("Examples") ff; // RAV1019
var x = 2 test // RAV1019

Line continuations

Line continuation is layout-sensitive and uses at most one newline.

Concept

When the parser still expects more of the current expression, one newline is treated as continuation trivia instead of as a statement terminator.

Example

val sum =
    1
    + offset

val labelled = 42 // comment stays with the literal
val next =
    labelled

val chain = source
    .Child
    .SubChild

val first = source.Call()

.Ok // starts a new target-typed expression (blank line breaks continuation)

x
+ 2     // same expression

x
.Foo()  // same expression

x

+ 2     // new statement

x

.Foo()  // new statement (member binding / target-typed form)

val a = 42
val b = 1; b = 3

Rules

  • One newline may continue the current expression.
  • Two or more consecutive newlines always terminate the current expression statement.
  • Continuation commonly occurs after assignment operators, before binary operators, and before member access (. or ->).
  • Indentation on the continued line remains trivia and does not change the semantics of the continued expression.

Detailed chapters

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