4 ms·

One of the problems with the old notation is the ambiguity. What does each of the following mean? n =- 5 n = -5 n=-5

hnlmorg 5y ago
Ahh yes, that’s a very good point.
mhh__ 5y ago
If I were designing a new language and where dead-set on the =- form I would make it so: n =- 5 // n equals n - 5 n = -5 // n equals -5 n=-5 //Illegal This can be done, it just requires getting the lexer right.
adrian_b 5y ago
Dennis Ritchie, in his paper about the history of C, explains that they became aware of these ambiguities only after the first C implementation, but they considered that it was a too big mistake, so they reversed the order in the next C version.
- Taniwha 5y ago
  maybe not quite the next version, from memory (and I ported compilers, and the kernels, for both) it was between v6 and v7 Unix
  - dn3500 5y ago
    That's correct, it wasn't the next version of the Ritchie compiler, it was a whole new compiler, the Portable C Compiler. It used yacc to generate the parser, and yacc complained about the ambiguity. They left the old syntax in for quite a while.
    - Taniwha 5y ago
      Yup, almost certainly PCC - which also still has struct fields in a global namespace as a (possible wonderful, possibly horrible) hack to provide the equivalent to unions
jandrese 5y ago
Another problem: n =* p; Is p a pointer or an integer? Maybe you want to do pointer math, it's a very C thing to do.
- jamesfinlayson 5y ago
  That was my thought too - seems like it would be ambiguous even with type information anyway as the readme says this iteration at least, any type can be converted to any other type.
moonchild 5y ago
The modern notation contains a very similar 'ambiguity'. Compare: x---y, x-- - y, and x - --y.
- mburee 5y ago
  And sadly x-----y won't parse :(
  - krylon 5y ago
    It's been a while I used C, but I for one am kind of glad that doesn't parse. If you need to do this, you can use parentheses: x - (--y) or (x--) - y
    - tom_ 5y ago
      All parse fine, and unambiguously, due to the maximal munch rule. x---y is (x--)-y, which is semantically valid. x-----y is ((x--)--)-y - but it's a semantic error, as x-- is not an lvalue.

Ahh yes, that’s a very good point.

If I were designing a new language and where dead-set on the =- form I would make it so: n =- 5 // n equals n - 5 n = -5 // n equals -5 n=-5 //Illegal This can be done, it just requires getting the lexer right.

adrian_b 5y ago

Dennis Ritchie, in his paper about the history of C, explains that they became aware of these ambiguities only after the first C implementation, but they considered that it was a too big mistake, so they reversed the order in the next C version.

Taniwha 5y ago
maybe not quite the next version, from memory (and I ported compilers, and the kernels, for both) it was between v6 and v7 Unix
- dn3500 5y ago
  That's correct, it wasn't the next version of the Ritchie compiler, it was a whole new compiler, the Portable C Compiler. It used yacc to generate the parser, and yacc complained about the ambiguity. They left the old syntax in for quite a while.
  - Taniwha 5y ago
    Yup, almost certainly PCC - which also still has struct fields in a global namespace as a (possible wonderful, possibly horrible) hack to provide the equivalent to unions

jandrese 5y ago

Another problem: n =* p; Is p a pointer or an integer? Maybe you want to do pointer math, it's a very C thing to do.

jamesfinlayson 5y ago
That was my thought too - seems like it would be ambiguous even with type information anyway as the readme says this iteration at least, any type can be converted to any other type.

moonchild 5y ago

The modern notation contains a very similar 'ambiguity'. Compare: x---y, x-- - y, and x - --y.

mburee 5y ago
And sadly x-----y won't parse :(
- krylon 5y ago
  It's been a while I used C, but I for one am kind of glad that doesn't parse. If you need to do this, you can use parentheses: x - (--y) or (x--) - y
  - tom_ 5y ago
    All parse fine, and unambiguously, due to the maximal munch rule. x---y is (x--)-y, which is semantically valid. x-----y is ((x--)--)-y - but it's a semantic error, as x-- is not an lvalue.