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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>Mu - exception2.mu</title> <meta name="Generator" content="Vim/8.0"> <meta name="plugin-version" content="vim7.4_v2"> <meta name="syntax" content="none"> <meta name="settings" content="number_lines,use_css,pre_wrap,no_foldcolumn,expand_tabs,line_ids,prevent_copy="> <meta name="colorscheme" content="minimal-light"> <style type="text/css">  </style> <script type='text/javascript'>  </script> </head> <body onload='JumpToLine();'> <a href='https://github.com/akkartik/mu/blob/master/exception2.mu'>https://github.com/akkartik/mu/blob/master/exception2.mu</a> <pre id='vimCodeElement'> 1 # Example program showing exceptions built out of delimited continuations. 2 # Slightly less klunky than exception1.mu. 3 4 # Since Mu is statically typed, we can't build an all-purpose higher-order 5 # function called 'try'; it wouldn't know how many arguments the function 6 # passed to it needs to take, what their types are, etc. Instead, until Mu 7 # gets macros we'll directly use the continuation primitives. 8 9 exclusive-container <a href='exception2.mu.html#L9'>error-or</a>:_elem [ 10 error:text 11 value:_elem 12 ] 13 14 def <a href='exception2.mu.html#L14'>main</a> [ 15 local-scope 16 <a href='exception2.mu.html#L21'>foo</a> false/no-exception 17 <a href='exception2.mu.html#L21'>foo</a> true/raise-exception 18 ] 19 20 # example showing exception handling 21 def <a href='exception2.mu.html#L21'>foo</a> raise-exception?:bool [ 22 local-scope 23 load-inputs 24 # To run an instruction of the form: 25 # try f ... 26 # write this: 27 # call-with-continuation-mark 999/exception-tag, f, ... 28 # By convention we reserve tag 999 for exceptions. 29 # 30 # The other inputs and outputs to 'call-with-continuation-mark' depend on 31 # the function it is called with. 32 _, result:<a href='exception2.mu.html#L9'>error-or</a>:num <- call-with-continuation-mark 999/exception-tag, <a href='exception2.mu.html#L47'>f</a>, raise-exception? 33 { 34 val:num, normal-exit?:bool <- maybe-convert result, value:variant 35 break-unless normal-exit? 36 $print [normal exit; result ] val 10/newline 37 } 38 { 39 err:text, error-exit?:bool <- maybe-convert result, error:variant 40 break-unless error-exit? 41 $print [error caught: ] err 10/newline 42 } 43 ] 44 45 # Callee function that we catch exceptions in must always return using a 46 # continuation. 47 def <a href='exception2.mu.html#L47'>f</a> raise-exception?:bool -> result:<a href='exception2.mu.html#L9'>error-or</a>:num [ 48 local-scope 49 load-inputs 50 { 51 break-unless raise-exception? 52 # throw/raise 53 result <- merge 0/error, [error will robinson!] 54 return-continuation-until-mark 999/exception-tag, result 55 } 56 # 'normal' return; still uses the continuation mark 57 result <- merge 1/value, 34 58 return-continuation-until-mark 999/exception-tag, result 59 # dead code just to avoid errors 60 result <- merge 1/value, 0 61 return result 62 ] </pre> </body> </html>


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