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.