Implement @tryswitch

[serenity4]

Implements @tryswitch as an extension to @switch where match failures are silent.

As mentioned in #131 we can move this implementation into a 3rd party library, but I think it is also convenient to have it alongside MLStyle.

[codecov]

Codecov Report

Merging #132 (d6b794e) into master (7bf8143) will increase coverage by 0.68%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master     #132      +/-   ##
==========================================
+ Coverage   81.94%   82.63%   +0.68%     
==========================================
  Files          26       26              
  Lines        1523     1589      +66     
==========================================
+ Hits         1248     1313      +65     
- Misses        275      276       +1     

Impacted Files	Coverage Δ
src/MatchImpl.jl	91.78% <85.71%> (-0.04%)	⬇️
src/AbstractPatterns/impl/RedyFlavoured.jl	91.75% <0.00%> (-0.10%)	⬇️
src/MatchCore.jl	5.50% <0.00%> (-0.06%)	⬇️
src/DeprecationUtils.jl	100.00% <0.00%> (ø)
src/StandardPatterns/WhenCases.jl	100.00% <0.00%> (ø)
src/AbstractPatterns/AbstractPatterns.jl	100.00% <0.00%> (ø)
src/AbstractPatterns/CaseMerge.jl	98.52% <0.00%> (+0.14%)	⬆️
src/Pervasives.jl	92.30% <0.00%> (+0.30%)	⬆️
src/Modules/AST.jl	84.78% <0.00%> (+0.33%)	⬆️
... and 9 more

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[Roger-luo]

since the PR is submitted here, maybe just have it in MLStyle? Expronicon is for meta-programming not the general case of pattern matching.

[thautwarm]

@Roger-luo A minor issue here is the implementation reuses @switch macro, hence the macro expands twice. Such operation can produce bad error messages when get used extensively.

[thautwarm]

I'd merge this now. Changes can be applied later. Thanks @serenity4 !

[serenity4]

@Roger-luo A minor issue here is the implementation reuses @switch macro, hence the macro expands twice. Such operation can produce bad error messages when get used extensively.

Ah, then we can just reuse the few lines of code for @switch (gen_switch and init_cfg). I thought reusing @switch would make it cleaner in terms of implementation. What is the problem with error messages? From a few local tests I couldn't see any issues with it.