Question

Whenever I define a function say funct(n), then can I assign value of n to a different variable such as m so that I can compare value of n which changes within the function with the initial value of m. Further, since I have nested and sometimes independent other functions, is there a way to make the m variable universal?

What I did is:

fun funct(n)= let val m=n in if (condition) then...

Further, here funct calls funct1 and funct1 calls funct2. The error message reads

Error: unbound variable or constructor: m

for funct2

Error: unbound variable or constructor: funct1

for funct1

Error: unbound variable or constructor: funct1

for funct

I suppose the single correction of m would solve the wholse cascade of errors.

Answer 1

You can access any identifier from scopes which are deeper than the one the identifer has been defined in. E.g.

fun funct(n) =
  let fun funct1(x, y, z) = if n < 1 then ...
  ...

In this example, funct1 has access to n, which has been defined in an outer scope (namely as a parameter of funct).

Be careful though, in functional languages like ML, identifiers have a different meaning from those in imperative languages like C. In your example, n and m are not variables, meaning the values denoted by the identifiers will not change. You can only redefine the identifiers; however, code that uses an identifier before its redefinition will always refer to the original value of that identifier.