[ANNOUNCEMENT] Try-Catch block

[LingDong-]

Hi everyone, as requested by #275 and #358 , try-catch is here! Here is an overview of the syntax:

姑妄行此。
	嗚呼。「「滅頂」」之禍。

如事不諧。豈「「ReferenceError」」之禍歟。
	吾有一言。曰「「本無此物。奈何用之」」。書之。

豈「「SyntaxError」」之禍歟。
	吾有一言。曰「「不合文法。不通之甚」」。書之。

豈「「TypeError」」之禍歟。
	吾有一言。曰「「物各其類。豈可混同」」。書之。

豈「「滅頂」」之禍歟。
	吾有一言。曰「「嗚呼哀哉。伏维尚飨」」。書之。

不知何禍歟。名之曰「奇禍」。
	吾有一言。曰「「人坐家中。禍從天降」」。書之。

乃作罷。

Which is roughly equivelent to this JavaScript:

try {
	var e = new Error(); e.name = "滅頂"; throw e;
} catch(e) {
	if (e.name == "ReferenceError") {console.log("本無此物。奈何用之")}
	else if (e.name == "SyntaxError") {console.log("不合文法。不通之甚")}
	else if (e.name == "TypeError") {console.log("物各其類。豈可混同")}
	else if (e.name == "滅頂") {console.log("嗚呼哀哉。伏维尚飨")}
	else {var err = e; console.log("人坐家中。禍從天降")}
}

If you do not need to catch the errors, you can do:

姑妄行此。
	嗚呼。「「無足輕重」」之禍。
如事不諧乃作罷。

Which roughly equals to:

try{
	var e = new Error(); e.name = "無足輕重"; throw e;
}catch(_){}

You can also do this to catch any error:

姑妄行此。
	嗚呼。「「事不關心」」之禍。
如事不諧。不知何禍歟。書之。乃作罷。

Which roughly equals to:

try{
	var e = new Error(); e.name = "事不關心"; throw e;
}catch(e){
	console.log(e);
}

You can see details about the usage in ./examples/try.wy.

Please let me know what you think or found any issues! Thanks a lot!

[liyishuai]

Is it a typo in JavaScript code that all conditions are the same?

[LingDong-]

Thanks @liyishuai you're right, just fixed the typo :P

[lymslive]

今天读到 Try-Catch.md 文档，感觉这语法句式设计挺有意境。
随即又感觉有两个字可以再推敲一下。

“姑妄行此” 我觉得用 “姑妄行是” 好此，用“是”表示“此”“如下”更有点古意。或者就按原 #275 的提议用”姑妄行之“。
“不知何禍歟”我觉得用“未知何禍歟”更有古意。
“如事不諧”倒是可以用“不”字，这比较顺畅惯用。既然这句用“不”字，再用“不知何祸”，两个“不”字有点犯重了。

当然，这已经是细枝末节了。
然后我更想说的是，switch case 语句，也可以参考这句式结构。case 语句与 catch 语句是非常似的。既然 catch 用“豈……歟”，那么 case用“其……歟“表达。

之前的 issue 有提到用”省“字表达 switch 含义。结合这里的语法，用”姑妄省之“，如何？

夫‘变量甲’，姑妄省之。
其……歟，乃
其……歟，乃
其……歟，乃
未知其数 // 未知其言
乃……
作罢

switch 限定只能用数字与字符串比较是可接受的。

也许”姑妄“用在 switch 语句中感觉太严重了，超级没底气的样子，与 try 也太过相似。那么用“如若省之”怎么样？这与 if 的“若”更亲缘。“若”关键字后接“省”就表示 switch 语义。

[LingDong-]

@lymslive , interesting suggestions!

• 此 and 是 are similar in both meaning and pronunciation (上聲四紙).
• 未 sounds like "not yet", while the final clause in try-catch is more "final".
• Indeed I intend to use a similar grammar for switch :)

[Lotayou]

@lymslive Guess the main reason @LingDong- don't use “姑妄行之” is that “之” has already been fixed as a keyword to reference the latest calculated/assigned variable.

[zxch3n]

Maybe this should be added to the syntax cheatsheet? @LingDong- @antfu

[antfu]

Good suggestion. It would be great if you can help out on our wiki https://github.com/wenyan-lang/wiki Thank you!