> In ML syntax, you don't know how many arguments a function will take, because of currying, and it's a (useful) feature, not a bug. Currying doesn't change th

> In ML syntax, you don't know how many arguments a function will take, because of currying, and it's a (useful) feature, not a bug. Currying doesn't change the picture here from the situation in, let's say, C. If it wasn't for "infixr", there would only be one way to parenthesise an expression. Just like in C, you could apply a function of N arguments to N+2 arguments, and the function call would get interpreted by the compiler as function application to N+2 arguments. It's just that there would be a type error, but gramatically, there is no ambiguity about which symbols are used as called functions, and which as arguments to the functions (and to which functions)... as long as you don't use "infixr". Same with a function of N+2 arguments getting N arguments. At some point you get a type error probably, because you're going to get a function, where you expected a non-function; but the type system doesn't influence the building of AST (in this place at least). Looking at the source you know how many arguments are getting applied to what, without even knowing the definitions of functions, as long as you don't play with infix functions. To make an example, again ignoring infix stuff, given "a b c d e", I know to read the whole expression as application of function a to arguments b, c, d, e. To be even more literal, SML doesn't have multiple-argument functions, all functions take one argument, and I can write it as "((((a b) c) d) e)". Unlike in concatenative languages, the function application doesn't suddenly stop in the middle of this expression, just because a takes fewer arguments than it was given, e.g. this expression can never be interpreted as "((a b) c) (d e)", even if it made more sense from the point of view of types of a, b, c, d, e. But when you do add infix syntax, then yeah, there is ambiguity, and now AST building is driven by the symbol table a bit.