Please, can you explain the following two features?
`unparse' in Spad
*****************
The program
-------------------------------------------- t.input
INT ==> Integer
show(xs : List INT) : String ==
oF := xs :: OutputForm
unparse(oF :: InputForm)
f(xs : List INT) : INT ==
empty? xs => 0
n := first xs
n < 2 => error concat["f ", show xs, " : first(arg) < 2."]
n + 1
--------------------------------------------
works in the interpreter. And its Spad analogue
-------------------------------------------------- t.spad
INT ==> Integer
)abbrev package FOO Foo
Foo() : with
show : List INT -> String
f : List INT -> INT
==
add
show(xs : List INT) : String ==
oF := xs :: OutputForm
unparse(oF :: InputForm)
f(xs : List INT) : INT ==
empty? xs => 0
n := first xs
n < 2 => error concat["f ", show xs, " : first(arg) < 2."]
n + 1
----------------------------------------------------------
does not compile. How to make it work, please?
Error messages
**************
I am looking into src/algebra/*.spad* in FriCAS-1.1.5 for the
examples of forming a message under applying `error'.
And the examples occur like this:
f(l : List Foo) : List Foo ==
empty? l => l
first(l) = 0 => error "first(l) = 0"
As I think, the error report will be like this:
Error in the library code:
first(l) = 0
It does not show in what function and of what package the break has
happened, and what are the responsible argument values.
What I am missing, please?
In Haskell, I write like this
f xs = let msg = showString "\nModule Foo, f " . shows xs .
showString "\n:\n"
in
if head xs == 0 then error $ msg "head xs == 0.\n"
else
...
Here the function msg :: String -> String is used in all the error
calls in the body of f, it presents a common prefix for these
messages. For example, f [0,3] breaks with the message
--------------------
Error ...
Module Foo, f [0,3]
:
head xs == 0.
--------------------
Respecively, my code of
... => error concat["f ", show xs, " : first(arg) < 2."]
is an attempt to follow this style in Spad
(but this `show' does not work).
What are your comments, please?
Thanks,
------
Sergei
[email protected]
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