93 lines
3 KiB
Standard ML
93 lines
3 KiB
Standard ML
//!/usr/bin/env fun
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/*
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* Debugging and error reporting demo for Fun.
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*
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* How to run:
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* fun --repl-on-error examples/debug_reporting.fun
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*
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* What happens:
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* - The program runs compute(), then triggers a runtime error in crash().
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* - The VM drops you into the REPL at the error site with the stack preserved.
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*
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* Try these REPL commands when it stops:
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* :backtrace # or :bt — show frames (most recent first)
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* :locals # locals in the current (top) frame
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* :stack # show the value stack
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* :top # show the top-of-stack value
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* :list # show source around the current line
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* :disas # disassemble around current instruction pointer (ip)
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* :frame 1 # select a lower frame, then try :locals, :list, :disas again
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* :printv local[0] # print a single value (also: stack[i], global[i])
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*
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* Stepping and breakpoints:
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* - Before re-running the script, you can set a breakpoint at the marker below.
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* For example (adjust the line number as needed in your copy):
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* :break examples/debug_reporting.fun:LINE_BK_1
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* :info breaks
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* :cont
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* On hit, try stepping:
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* :step # step one instruction
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* :next # step over
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* :finish # run until current frame returns
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* :cont # continue until next stop (breakpoint or error)
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*
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* Note: If line numbers drift due to edits, use :list and :backtrace to locate the desired spot,
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* then set the breakpoint with the correct file:line.
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*/
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/* A small helper computation to set a breakpoint on */
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fun add(a, b)
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// Simple arithmetic to have a few instructions to step over
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c = a + b
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print(c)
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/* A function that calls add() and has a good place for a breakpoint */
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fun compute(n)
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arr = [10, 20, 30, 40, 50]
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i = 2
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// BREAKPOINT CANDIDATE (LINE_BK_1): set a breakpoint on the next line:
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x = arr[i] + 7
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add(x, n)
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/* A function that intentionally triggers a runtime error (index out of range) */
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fun crash()
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nums = [1, 2, 3]
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// This out-of-range access triggers an error and drops into the REPL:
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print(nums[10])
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fun main()
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compute(3)
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crash()
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main()
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/* Expected when run with --repl-on-error (your version and line/ip may vary):
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Runtime error: index out of range
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(at ./examples/debug_reporting.fun:XX in crash, op INDEX_GET @ip YY)
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Entering REPL due to runtime error (code 1)
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Fun VERSION REPL
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Type :help for commands. Submit an empty line to run.
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fun> :backtrace
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Backtrace (most recent call first):
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#TOP crash at ./examples/debug_reporting.fun ip=... line=...
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#... main at ./examples/debug_reporting.fun ip=... line=...
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fun> :list
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> <current line> ...
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fun> :locals
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0: [locals if any]
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fun> :disas
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> ip: OP_NAME OPERAND
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...
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fun> :stack
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[... stack values ...]
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Then try breakpoints and stepping on a new run:
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fun> :break ./examples/debug_reporting.fun:<line for LINE_BK_1>
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fun> :info breaks
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fun> :cont
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... Breakpoint hit ...
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fun> :next
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fun> :finish
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fun> :cont
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*/
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