Common Lisp like condition system for Julia
Start with the docstring of @handler_case to see how this works ...
help?> @handler_case
Convenience macro around handler_bind which works similar to try-catch, i.e., the first matching handler is run with the stack unwound and its result is returned.
Examples
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julia> @handler_case @signal(3.0) begin
Integer => c -> (:integer, c)
Number => c -> (:number, c)
Any => c -> (:any, c)
end
(:number, 3.0)
See also @signal, handler_bind as well as nonlocal and jump.Features
-
@signaldoes not unwind the stack, i.e., in contrast tothrow -
Restarts allow to continue execution higher up in the stack
Thinks to try
Use interactive setup and drop into Infiltrator where a condition was signalled!
using Conditions
toggle_interactive(true)
h(z) = @signal z
g(y) = h(y + 2)
f(x) = g(2 * x)
f(3)
# Try @trace and @locals from the infiltration prompt! Restarts are the real deal and allow top-level code decide how to fix stuff higher up on the stack!
using Conditions
function nonneg(x::Number)
if x >= 0
x
else
@signal ArgumentError("Negative $x")
end
end
function validate(x::Number)
@restart_case nonneg(x) begin
:fix_value => newval -> newval
end
end
function mysum(xs::AbstractVector)
@restart_case sum(validate, xs) begin
:rough_guess => () -> 42
end
end
# Restart functions
function fix_value(condition)
fixme = find_restart(:fix_value)
if !isnothing(fixme)
fixval = 2
println("Fixing $(condition.msg) into $fixval")
invoke_restart(fixme, fixval)
end
end
function rough_guess(condition)
guess = find_restart(:rough_guess)
if !isnothing(guess)
println("Guessing total after $condition")
invoke_restart(guess)
end
end
xs = [1, 2, -1, 3, 4, -5, 0]
# Top-level handler decides what to do
handler_bind(Handler(ArgumentError, fix_value)) do
mysum(xs)
end
handler_bind(Handler(ArgumentError, rough_guess)) do
mysum(xs)
end