Scheme nested lambda function

Question

I am a beginner in Scheme. I found this question in MIT exam 1 for SICP lecture.

What's the value and type for –

((lambda (a) (lambda (b) (+ (sqrt a) (sqrt b)))) 5)

I am having a hard time understanding how this function works. I am really confused about the parameter b. Only 5 is passed as a parameter to the outer lambda function, then what value does b take for the inner lambda function?

I tried running this function in mit-scheme but the resulting value gets incremented each time it's run.

Jeff Ames · Accepted Answer · 2015-05-23 05:26:35Z

2

You're correct that only the outer lambda form is applied to the argument 5. Then it returns its body with a replaced with 5, so it would return

(lambda (b) (+ (sqrt 5) (sqrt b)))

which is itself a function. This could later be applied to another argument, to produce an actual numeric value.

answered May 23, 2015 at 5:26

Jeff Ames

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2 Comments

lonewolf Over a year ago

When i run the code in mit-scheme i am getting result as follows Value 13: #[compound-procedure 13] . What is value 13 here? When i run the code again the value gets incremented as Value 14:#[compound-procedure 14]. Why does this happen?

Jeff Ames Over a year ago

It sounds like those might just be unique IDs generated for each procedure.

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