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Uncaught Bind exception in compiler with opaque signature matching #289
Description
Version
110.99.4 (Latest)
Operating System
- Any
- Linux
- macOS
- Windows
- Other Unix
OS Version
No response
Processor
- Any
- Arm (using Rosetta)
- PowerPC
- Sparc
- x86 (32-bit)
- x86-64 (64-bit)
- Other
System Component
Core system
Severity
Minor
Description
The elaborator raises a Bind exception when dealing with a structure that has type errors and an opaque signature.
Transcript
% sml bug.sml
Standard ML of New Jersey (64-bit) v110.99.4 [built: Tue Aug 01 16:07:38 2023]
[opening bug.sml]
[autoloading]
[library $SMLNJ-BASIS/basis.cm is stable]
[library $SMLNJ-BASIS/(basis.cm):basis-common.cm is stable]
[autoloading done]
bug.sml:41.32-43.37 Error: types of rules do not agree [circularity]
earlier rule(s): ('Z -> 'Y) result -> 'Y result
this rule: ('Z -> 'Y) result -> ('Z -> 'Y) result
in rule:
err => err
bug.sml:1.2-52.6 Error: value type in structure does not match signature spec
name: field
spec: string
-> 'a ?.JSONDecode.decoder
-> ('a -> 'b) ?.JSONDecode.decoder -> 'b ?.JSONDecode.decoder
actual: string
-> 'a ?.JSONDecode.decoder
-> ('a -> 'a) ?.JSONDecode.decoder -> 'a ?.JSONDecode.decoder
uncaught exception Bind [nonexhaustive binding failure]
raised at: ../compiler/Elaborator/elaborate/elabmod.sml:624.13-624.67
../compiler/Elaborator/elaborate/elabmod.sml:1363.32
../compiler/Basics/stats/stats.sml:198.40
../compiler/TopLevel/interact/evalloop.sml:45.54
../compiler/TopLevel/interact/evalloop.sml:306.20-306.23
Expected Behavior
There should not be an uncaught Bind exception.
Steps to Reproduce
Here is the source that reproduces the bug:
structure JSONDecode :> sig
datatype 'a result = Err of exn | Ok of 'a
type 'a decoder
(* decode a required field *)
val field : string -> 'a decoder -> ('a -> 'b) decoder -> 'b decoder
end = struct
datatype value
= OBJECT of (string * value) list
| ARRAY of value list
| NULL
| BOOL of bool
| INT of IntInf.int
| FLOAT of real
| STRING of string
exception FieldNotFound of value * string
exception NotObject of value
fun lookupField (v as OBJECT fields) = let
fun find lab = (case List.find (fn (l, v) => (l = lab)) fields
of NONE => raise FieldNotFound(v, concat["no definition for field \"", lab, "\""])
| SOME(_, v) => v
(* end case *))
in
find
end
| lookupField v = raise NotObject v
datatype 'a result = Err of exn | Ok of 'a
datatype 'a decoder = D of value -> 'a result
(* decode a required field *)
fun field key (D valueDecoder) (D objDecoder) = let
fun decoder jv = (case valueDecoder (lookupField jv key)
of Ok fld => (case objDecoder jv
of Ok mkObj => Ok(mkObj fld)
| err => err
(* end case *))
| err => err
(* end case *))
handle ex => Err ex
in
D decoder
end
endAdditional Information
Note that changing the :> to : for the signature ascription causes the bug to disappear.
Activity
[-]uncaught Bind exception in compiler with opaque signature matching[/-][+]Uncaught `Bind` exception in compiler with opaque signature matching[/+]dmacqueen commentedon Feb 7, 2024
This issue (bug) seems to be closely related to issue 285 (Bind exception after a static signature matching error). Here is a much simpler test case that produces the Bind exception behavior.
dmacqueen commentedon Feb 7, 2024
There is a fairly mild fix to elabmod.sml and sigmatch.sml involving having SigMatch.matchStr return an option result which would be NONE in the case that the signature match fails, instead of a "bogus" record. This fix eliminates the uncaught Bind exceptions in Issues $285 and #289, but it has an unexpected side effect of not allowing the legacy compiler to bootstrap with an unbound lambda var exception during the init phase when compiling dummy.sml. So this weird side effect would need to be fixed before the fix could be committed.
attempted fix for #285 and #289, bootstrap fails in init compiling du…
fix for Issues #285, #289 (uncaught Bind after sigmatch failure
dmacqueen commentedon Mar 5, 2024
Committed a second, successful fix for #285 and #289. This fix introduces another severity constructor for ErrorMsg.severity, "TERMINAL". When this severity is passed to the ErrorMsg.error function, the error message is printed and ErrorMsg.Error is raised, terminating compilation. So for the two modes of signature matching failure represented by #285 (unmatched spec) and #289 (val spec type mismatch), there is no attempt to recover after the error by returning a bogus result from sigMatch. WARNING: there are several other signature matching failure modes whose treatment has not changed, so there may be other cases where recovery is attempted after a signature match failure, leading to an uncaught BIND exception in the function constrStr function in ElabMod. A full fix needs to deal with all signature match failure modes in Elaborator/modules/sigmatch.sml.