Question

I noticed that the optional parentheses in Coffeescript introduce a syntactic ambiguity.
For example, the code

prompt Math.max(2), 3      # no space after max

compiles to

prompt(Math.max(2), 3);    // one parameter to max(), two to prompt()

whereas

prompt Math.max (2), 3     # space after max

compiles to

prompt(Math.max(2., 3));    // two parameters to max(), one to prompt()

I.e. adding a space before the parameter list changes the grouping of the parameters.

Is this intentional? Are there other places in the language where a space makes a syntactic difference?

Answer 1

Yes, it is intentional.

Space after variable in CofeeScript means: “apply the following list of arguments to this function.

Lets look to your code:

prompt Math.max(2), 3

It means: “apply to prompt two arguments: Math.max(2) and 3“.

prompt Math.max (2), 3

It means: “apply to Math.max two arguments: (2) and 3, and then apply the result to prompt“.

Lets see more complex example:

my_function (obj = other_function 1, 2), some_var

In this example bracket are necessary.

This feature allows you to write the same code in two ways:

my_function (my_array.map (x) -> do_smth x), some_var

is the same as

my_function my_array.map((x) -> do_smth x), some_var

I don’t know about any other places in the language, where a space makes a syntactic difference. But there is a place, where brackets makes difference:

my_object = one: two: three: 'three', four: 'four'
=>
my_object = {one: {two: {three: 'three', four: 'four'}}}

and

my_object = one: {two: three: 'three'}, four: 'four'
=>
my_object = {one: {two: {three: 'three'}, four: 'four'}}