let 用来引入新的本地变量

[panfei]

let所指定的变量不是全局的，而是本地的：

[7]> (let ((x 1) (y 2)))

NIL

[8]> x

*** - SYSTEM::READ-EVAL-PRINT: variable X has no value

The following restarts are available:

USE-VALUE      :R1      Input a value to be used instead of X.

STORE-VALUE    :R2      Input a new value for X.

ABORT          :R3      Abort main loop

Break 1 [9]> :R3

[10]> (+ x y)

*** - SYSTEM::READ-EVAL-PRINT: variable X has no value

The following restarts are available:

USE-VALUE      :R1      Input a value to be used instead of X.

STORE-VALUE    :R2      Input a new value for X.

ABORT          :R3      Abort main loop

Break 1 [11]> :R3

[12]> (let ((x 1) (y 2))

(+ x y))

3

[13]> (+ x y)

*** - SYSTEM::READ-EVAL-PRINT: variable X has no value

The following restarts are available:

USE-VALUE      :R1      Input a value to be used instead of X.

STORE-VALUE    :R2      Input a new value for X.

ABORT          :R3      Abort main loop

Break 1 [14]> :R3

[15]> 

--
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