Annotation of gforth/except.fs, revision 1.10
1.1 anton 1: \ catch, throw, etc.
2:
1.7 anton 3: \ Copyright (C) 1999,2000,2003 Free Software Foundation, Inc.
1.1 anton 4:
5: \ This file is part of Gforth.
6:
7: \ Gforth is free software; you can redistribute it and/or
8: \ modify it under the terms of the GNU General Public License
9: \ as published by the Free Software Foundation; either version 2
10: \ of the License, or (at your option) any later version.
11:
12: \ This program is distributed in the hope that it will be useful,
13: \ but WITHOUT ANY WARRANTY; without even the implied warranty of
14: \ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15: \ GNU General Public License for more details.
16:
17: \ You should have received a copy of the GNU General Public License
18: \ along with this program; if not, write to the Free Software
1.3 anton 19: \ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
1.1 anton 20:
21: \ !! use a separate exception stack? anton
22:
23: \ user-definable rollback actions
24:
25: Defer 'catch
26: Defer 'throw
27:
28: ' noop IS 'catch
29: ' noop IS 'throw
30:
31: \ has? backtrace [IF]
32: Defer store-backtrace
33: ' noop IS store-backtrace
34: \ [THEN]
35:
1.9 anton 36: \ Ok, here's the story about how we get to the native code for the
37: \ recovery code in case of a THROW, and why there is all this funny
38: \ stuff being compiled by TRY and RECOVER:
39:
40: \ Upon a THROW, we cannot just return through the ordinary return
41: \ address, but have to use a different one, for code after the
42: \ RECOVER. How do we do that, in a way portable between the various
43: \ threaded and native code engines? In particular, how does the
44: \ native code engine learn about the address of the native recovery
45: \ code?
46:
47: \ On the Forth level, we can compile only references to threaded code.
48: \ The only thing that translates a threaded code address to a native
49: \ code address is docol, which is only called with EXECUTE and
50: \ friends. So we start the recovery code with a docol, and invoke it
51: \ with PERFORM; the recovery code then rdrops the superfluously
52: \ generated return address and continues with the proper recovery
53: \ code.
54:
55: \ At compile time, since we cannot compile a forward reference (to the
56: \ recovery code) as a literal (backpatching does not work for
57: \ native-code literals), we produce a data cell (wrapped in AHEAD
58: \ ... THEN) that we can backpatch, and compile the address of that as
59: \ literal.
60:
61: \ Overall, this leads to the following resulting code:
62:
63: \ ahead
64: \ +><recovery address>-+
65: \ | then |
66: \ +-lit |
67: \ (try) |
68: \ ... |
69: \ (recover) |
70: \ ahead |
71: \ docol: <-----------+
72: \ rdrop
73: \ ...
74: \ then
75: \ ...
76:
77: \ !! explain handler on-stack structure
78:
1.5 anton 79: : (try) ( ahandler -- )
1.1 anton 80: r>
1.5 anton 81: swap >r \ recovery address
1.1 anton 82: rp@ 'catch >r
83: sp@ >r
84: fp@ >r
85: lp@ >r
86: handler @ >r
87: rp@ handler !
1.5 anton 88: >r ;
1.1 anton 89:
90: : try ( compilation -- orig ; run-time -- ) \ gforth
1.5 anton 91: \ !! does not work correctly for gforth-native
1.8 anton 92: POSTPONE ahead here >r >mark 1 cs-roll POSTPONE then
1.9 anton 93: r> POSTPONE literal POSTPONE (try) ; immediate compile-only
1.1 anton 94:
95: : (recover) ( -- )
96: \ normal end of try block: restore handler, forget rest
97: r>
98: r> handler !
99: rdrop \ lp
100: rdrop \ fp
101: rdrop \ sp
102: r> rp!
103: rdrop \ recovery address
104: >r ;
105:
106: : recover ( compilation orig1 -- orig2 ; run-time -- ) \ gforth
107: \ !! check using a special tag
108: POSTPONE (recover)
1.9 anton 109: POSTPONE else
110: docol: here 0 , 0 , code-address! \ start a colon def
111: postpone rdrop \ drop the return address
112: ; immediate compile-only
1.1 anton 113:
114: : endtry ( compilation orig -- ; run-time -- ) \ gforth
115: POSTPONE then ; immediate compile-only
116:
117: :noname ( x1 .. xn xt -- y1 .. ym 0 / z1 .. zn error ) \ exception
118: try
119: execute 0
120: recover
121: nip
122: endtry ;
123: is catch
124:
125: :noname ( y1 .. ym error/0 -- y1 .. ym / z1 .. zn error ) \ exception
126: ?DUP IF
127: [ here forthstart 9 cells + ! ]
1.10 ! pazsan 128: store-backtrace error-stack off
1.1 anton 129: handler @ ?dup-0=-IF
1.6 anton 130: >stderr cr ." uncaught exception: " .error cr
1.1 anton 131: 2 (bye)
1.6 anton 132: \ quit
1.1 anton 133: THEN
134: rp!
135: r> handler !
136: r> lp!
137: r> fp!
138: r> swap >r sp! drop r>
1.9 anton 139: rdrop 'throw r> perform
1.1 anton 140: THEN ;
141: is throw
1.10 ! pazsan 142: [IFDEF] throw>error
! 143: :noname ( y1 .. ym error/0 -- y1 .. ym / z1 .. zn error ) \ exception
! 144: ?DUP IF
! 145: handler @ ?dup-0=-IF
! 146: >stderr cr ." uncaught exception: " .error cr
! 147: 2 (bye)
! 148: \ quit
! 149: THEN
! 150: rp!
! 151: r> handler !
! 152: r> lp!
! 153: r> fp!
! 154: r> swap >r sp! drop r>
! 155: rdrop 'throw r> perform
! 156: THEN ;
! 157: is throw>error
! 158: [THEN]
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