let

code: eval.c

DEFUN ("let", Flet, Slet, 1, UNEVALLED, 0,

doc: /* Bind variables according to VARLIST then eval BODY.

The value of the last form in BODY is returned.

Each element of VARLIST is a symbol (which is bound to nil)

or a list (SYMBOL VALUEFORM) (which binds SYMBOL to the value of VALUEFORM).

All the VALUEFORMs are evalled before any symbols are bound.

usage: (let VARLIST BODY...) */)

(Lisp_Object args)

{

Lisp_Object *temps, tem, lexenv;

Lisp_Object elt;

ptrdiff_t count = SPECPDL_INDEX ();

ptrdiff_t argnum;

USE_SAFE_ALLOCA;

Lisp_Object varlist = XCAR (args);

/* Make space to hold the values to give the bound variables. */

EMACS_INT varlist_len = list_length (varlist);

SAFE_ALLOCA_LISP (temps, varlist_len);

ptrdiff_t nvars = varlist_len;

/* Compute the values and store them in `temps'. */

for (argnum = 0; argnum < nvars && CONSP (varlist); argnum++)

{

maybe_quit ();

elt = XCAR (varlist);

varlist = XCDR (varlist);

if (SYMBOLP (elt))

else if (! NILP (Fcdr (Fcdr (elt))))

signal_error ("`let' bindings can have only one value-form", elt);

else

}

nvars = argnum;

lexenv = Vinternal_interpreter_environment;

varlist = XCAR (args);

for (argnum = 0; argnum < nvars && CONSP (varlist); argnum++)

{

Lisp_Object var;

elt = XCAR (varlist);

varlist = XCDR (varlist);

var = SYMBOLP (elt) ? elt : Fcar (elt);

if (!NILP (lexenv) && SYMBOLP (var)

&& !XSYMBOL (var)->u.s.declared_special

&& NILP (Fmemq (var, Vinternal_interpreter_environment)))

/* Lexically bind VAR by adding it to the lexenv alist. */

lexenv = Fcons (Fcons (var, tem), lexenv);

else

/* Dynamically bind VAR. */

specbind (var, tem);

}

if (!EQ (lexenv, Vinternal_interpreter_environment))

/* Instantiate a new lexical environment. */

specbind (Qinternal_interpreter_environment, lexenv);

elt = Fprogn (XCDR (args));

return SAFE_FREE_UNBIND_TO (count, elt);

}