Understanding "let" expression in LISP -


i extremely new lisp, had previous experience functional programming (haskell, sml). why code returning 14, , not 10 (ie. 1 + 2y + 3 + 1)?

(defvar x 1)  (defun g (z)   (+ x z))  (defun f (y)   (+ (g 1)      (let ((x (+ y 3)))         (g (+ y x)))))  (f 2)

because used (defvar x 1), declares x global special variable. causes every other later binding of x use dynamic binding: here in (let ((x ....

style & convention in lisp

convention in lisp: use *x* instead of x special variables.

(defvar *x* 1)

your code is:

(defvar *x* 1)   ; global special variable *x*  (defun g (z)   (+ *x* z))     ; use special variable *x*  (defun f (y)   (+ (g 1)      (let ((x (+ y 3)))    ; lexical binding of x         (g (+ y x)))))     ; use lexical binding of x

run:

? (f 2) 10

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