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F# / Collections

List.fold

Learn List.fold in F# through a focused explanation, a dedicated topic-specific example, an engineering boundary, and a mastery check.

12 min read • Intermediate

List.fold is a focused F# lesson inside Collections. The example uses the construct named in the lesson directly rather than reusing a generic placeholder.

Trace the example from its inputs through List.fold and identify the behavior that would change if that construct were removed or replaced. Pay attention to the language-specific rules shown by the syntax, because neighboring lessons intentionally exercise different mechanisms.

Topic-specific example

fsharp-0036-7102fb78ad.fsx
fsharp Try It Live 
let values37 = [37; 38; 39]
printfn "%d" (List.sum values37) // List.fold
Edge case / engineering note

For List.fold, test one realistic boundary: empty data, invalid input, unavailable resources, lifetime/cleanup, type constraints, or concurrency timing where applicable. A successful happy path is not enough to prove the construct is used correctly.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

List.fold Mastery Check →
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