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#### 5.3.3 Function Bindings

These forms make `let`-like bindings to functions instead of variables.

— Special Form: flet (bindings...) forms...

> This form establishes `let`-style bindings on the function cells of symbols rather than on the value cells. Each binding must be a list of the form ‘`(name arglist forms...)`’, which defines a function exactly as if it were a `defun*` form. The function name is defined accordingly for the duration of the body of the `flet`; then the old function definition, or lack thereof, is restored.

> While `flet` in Common Lisp establishes a lexical binding of name, Emacs Lisp `flet` makes a dynamic binding. The result is that `flet` affects indirect calls to a function as well as calls directly inside the `flet` form itself.

> You can use `flet` to disable or modify the behavior of a function in a temporary fashion. This will even work on Emacs primitives, although note that some calls to primitive functions internal to Emacs are made without going through the symbol's function cell, and so will not be affected by `flet`. For example,

>               (flet ((message (&rest args) (push args saved-msgs)))
>                 (do-something))

> This code attempts to replace the built-in function `message` with a function that simply saves the messages in a list rather than displaying them. The original definition of `message` will be restored after `do-something` exits. This code will work fine on messages generated by other Lisp code, but messages generated directly inside Emacs will not be caught since they make direct C-language calls to the message routines rather than going through the Lisp `message` function.

> Also note that many primitives (e.g. `+`) have special byte-compile handling. Attempts to redefine such functions using `flet` will fail if byte-compiled. In such cases, use `labels` instead.

> Functions defined by `flet` may use the full Common Lisp argument notation supported by `defun*`; also, the function body is enclosed in an implicit block as if by `defun*`. See Program Structure.

— Special Form: labels (bindings...) forms...

> The `labels` form is like `flet`, except that it makes lexical bindings of the function names rather than dynamic bindings. (In true Common Lisp, both `flet` and `labels` make lexical bindings of slightly different sorts; since Emacs Lisp is dynamically bound by default, it seemed more appropriate for `flet` also to use dynamic binding. The `labels` form, with its lexical binding, is fully compatible with Common Lisp.)

> Lexical scoping means that all references to the named functions must appear physically within the body of the `labels` form. References may appear both in the body forms of `labels` itself, and in the bodies of the functions themselves. Thus, `labels` can define local recursive functions, or mutually-recursive sets of functions.

> A “reference” to a function name is either a call to that function, or a use of its name quoted by `quote` or `function` to be passed on to, say, `mapcar`.