With more words: I have written a parser and type checker for an ML-style language, with parametric types and several other neat tricks in it, and I've now written a parser and type checker for a good subset of Go. The latter has been far more work. I am not entirely sure how to explain the work. Go has lots of syntactic and type conveniences that are easy to use and read, but quite difficult to implement.
As there are few implementers and many users, I think the original designers of Go picked well when they put the work on us implementers.
In particular note the difference between
const hello = "Hello, 世界"
const typedHello string = "Hello, 世界"
As a user of Go I find untyped constants to be extremely useful. They almost always do what I want without surprise. Implementing them however, is not trivial.
A tricker example is embedding. It adds a lot of complexity to the type system. As a user, it can be a bit surprising, but I admit it is very useful.
Languages that have simpler syntax tend to have far more complex semantics (to infer what's missing, etc.).
Eg. python's semantics is horribly complex: "hello".upper() is something like str.__dict__['upper']("hello")) -- which is all run-time. Whereas say a C++ version amounts to quite a simple run-time function call on some bytes.
First is the fact that the top level is statements, not declarations. That would mean heavy modification to the go/parser package to make the inner-function statement parser the top level.
Second is the fact I need to parse incrementally, to implement a REPL. That would not require serious modification to go/parser, but it would to go/types.
Third is I wanted to experiment with new syntax. It was quicker to get to that experimentation by working from scratch rather than adopting go/parser and go/types.
Fourth is there are some fundamental things I would like to do differently, particularly around how comments are handled. I haven't got there yet.
In retrospect, if the new Go parser inside cmd/compile existed when I started this, I probably would have started from there. (It does many of the things I wanted to do to go/parser.) I suspect I still would have ended up with my own type checker though, if for no other reason than incremental type checking.
I'll have to try it out.
Let's look at some of Java's keywords which have no analogue in the Go specification's list of keywords
1. boolean: go has the `bool` type, but it's a builtin, not a keyword, so it doesn't count against it.
2. byte: same thing
3. null: Go's `nil` is again not counted as a keyword in their list of 25
....
And hey, that accounts for almost the entire difference if you count all the primitive types.
Go, on the other hand, does not consider those "keywords", which leads to absolutely silly behaviour.
A programmer can accidentally redefine `len` to be a variable, and then `len(x)` will be an error later.
Because go has a ton of important builtins which aren't reserved keywords, you can write incredibly confusing code:
https://play.golang.org/p/-xChCblMEh
For a nice list, check out https://play.golang.org/p/yjkxqVY4eo
... yeah, Go's small number of keywords is often touted by Gophers, but really it's because the go team made this incredibly stupid decision.
If you counted the same sorts of things as keywords that java did, Go would have almost exactly the same number... and more problems would be caught at compile-time (like `len := 1`) .
Whenever a difference is found between the two Go compilers, gccgo and gc, the spec is consulted to see which is right. If the spec is not clear on which compiler is right, then the spec is changed so it is.
When the third frontend was written (go/parser and go/types in the standard library), the spec played a similar role. Though far fewer changes were made to the spec, suggesting it is getting pretty good.
Java has 53 keywords, whereas Go has 25 keywords and 39 special identifiers, totalling 64, a little more than Java's but less than C#'s 78.
I appreciate the sentiment – that there's a lot of work left to do – but isn't the assertion about syntax size false? I thought Go's syntax was quite small compared to other popular languages? It only has 25 reserved words (Java has 50+) and was designed in part to be uniform and easy to read.