<-

<- appears inside do notation. It runs a monadic action and binds its inner value to a name for the rest of the block.

Syntax

(do
  ...
  (⟨var⟩ <- ⟨expr⟩)
  ...)

Semantics

• (⟨var⟩ <- ⟨expr⟩) is do notation for a monadic bind.
• Under the hood it expands to a monadic bind using the standard library.
• The bound name is in scope for the remaining forms in the block.

Example

(do
  (a <- ax)
  (b <- bx)
  (pure (+ a b)))