[Haskell-cafe] Bound and free variables

[Emil Axelsson]

[The previous message went off prematurely.]

I think bound and free usually refers to *occurrences* of variables in 
an expression. In your example you only have occurrences of g and c, but 
there may be more hiding in the ... part.

A variable is free in an expression if the path from the root to the 
variable does not include a binder for the variable. In your example, g 
is bound in the whole expression, but free in the sub-expression g c.

However, I think that "bound" is also sometimes used to mean "in scope", 
and this seems to be mainly your interpretation. When you say "y is 
bound in g", you really mean that y is in scope in *the body* of g (i.e. 
in the ...), or, alternatively that every occurrence of y in the body of 
g is bound.

(IIUC...)

/ Emil

Den 2014-09-18 08:49, Jan Stolarek skrev:
> Hi *,
>
> I have a simple question about terminology regarding bound and free variables. Assume I have:
>
> let f x  = let g y = ...
>              in g c
> in ...
>
> Now:
>    - `c` is free in `g` and `f`
>    - `y` is bound in `g`
>    - `x` is free in `g`.
>    - `x` is bound in `f`
>
> What about `y` in `f`? Is it also bound in `f`? If so then it certainly is bound in a different
> way that `x`. Is there a terminology that allows to distinguish these different forms of bound
> variables?
>
> Janek
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