> For the complete documentation index, see [llms.txt](https://mandober.gitbook.io/math-debrief/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mandober.gitbook.io/math-debrief/340-lambda-calculi/terms/let-expression.md).

# Let expression

<https://en.wikipedia.org/wiki/Let_expression>

* `let` expression associates a function definition with a *restricted scope*
* in LC, `let` expression is a lambda abstraction applied to an arg
* in math, `let` expr associates a Boolean condition with a restricted scope
* in math, let expression may be considered as a conjunction of expressions, within an existential quantifier which restricts the scope of the variable.
* let expression is present in many FPL to allow the *local definition* of expression, for use in defining another expression.
* `let rec` is an extension of the simple let expression which uses the fixed-point combinator to implement recursion.