I got the following code:
g = lambda x: x+7
foo = lambda f: (lambda x: f(x+1)*2)
print( g(3), (foo(g))(3), (foo(foo(g))((3) )
Could I get an explanation on how (foo(foo(g))((3) works?
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1 Answer
The first thing to remember is that lambdas are regular functions that:
- Don't automatically have names
- Can be used as expressions
- Must consist of a single expression
- Implicitly
returnthe results of that expression
So you can always rewrite them as normal def functions with names if you're confused. For example, foo can become:
def foo(f):
def foo_inner(x):
return f(x + 1) * 2
return foo_inner
So calling foo with any function (f) returns a new function which takes a numeric type, adds one to it, calls f with the value, and doubles the result.
All the rest of it is just tracing the multiple layers of wrapping here, which I'll leave to you; this isn't an interesting problem in general. In real code that uses factory functions like this, the intent and behavior is generally much more clear (because it's being done for a purpose, rather than as a brainteaser).