为何F#重新定义部分通用编程标准？技术缘由问询

Hey Thomas, awesome questions—these design choices aren’t just arbitrary quirks; they’re tied to F#’s functional-first roots, parsing efficiency, and consistency with its ML-language heritage. Let’s break down each one with technical context:

First off, this comes directly from F#’s lineage in the ML family (think OCaml, Standard ML), which has used parenthesized star comments for decades. Beyond tradition, there’s a practical technical benefit: nested comments. Unlike /* */ (which breaks if you nest /* comment /* nested */ */ in most languages), (* *) supports safe nesting. This is incredibly useful for functional code, where you might want to comment out large blocks that already contain comments, or document nested expressions.

Additionally, F# treats / as a first-class operator (for division). Using /* could introduce parsing ambiguities in edge cases—for example, a/*b might be misinterpreted as a / *b (division followed by a pointer-like dereference, even though F# doesn’t have pointers, the parser would still need to resolve the ambiguity). The (* syntax avoids this entirely.

F# is a type-inferred language first—most of the time, you don’t even need to specify a type (e.g., let x = 5 is automatically inferred as int). Putting the type as a suffix makes this optional syntax feel natural, rather than forcing you to write redundant type information upfront.

From a parsing perspective, functional languages prioritize expressions over statements. Writing name : type aligns with how F#’s type checker works: it infers types from the expression on the right-hand side, then associates that type with the name. This flow (name ← expression ← type) is more intuitive for the compiler’s inference engine.

Also, this syntax matches how function types are written in F#. For example, a function taking an int and returning a string is written as int -> string—so declaring a function as let f : int -> string = fun x -> string x keeps the type annotation consistent with the language’s core type syntax.

Again, this is rooted in ML tradition, but there’s a parsing angle too. In F#, ! is a unary operator used to dereference mutable references (e.g., let r = ref 10; printfn "%d" !r). Using != could create ambiguity in code like !x != y—would that mean "the value of reference x is not equal to y" or "x not equal to y"? While the parser could resolve this with operator precedence, <> avoids the confusion entirely.

Plus, <> aligns more closely with mathematical notation (it’s a visual stand-in for ≠), which fits F#’s focus on mathematical and functional programming patterns.

F# defaults to immutability, so the simplest symbol (=) is reserved for binding—creating a new immutable name-value pair (this isn’t "assignment" in the imperative sense; it’s a definition). The <- operator is explicitly for mutating an existing variable (like updating a mutable let mutable x or a record field).

This deliberate distinction serves two technical purposes:

1. Parsing clarity: The compiler can immediately tell whether you’re defining a new binding or modifying an existing mutable value, no extra context needed.
2. Code readability: Mutable operations stand out in the codebase, which encourages developers to use immutability by default (a core functional programming principle).

内容的提问来源于stack exchange，提问作者Thomas