type checking ambiguities

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type checking ambiguities #877

Open jgroote opened 12 years ago

jgroote commented 12 years ago

Issue migrated from trac ticket # 874

component: Core: Type-checker Library | priority: major

2011-11-24 14:33:23: @wiegerw created the issue

In the following example from Jaco van de Pol there is an ambiguity in the types of the action labels:

act welke:Nat; welke:Int;

init welke(0) + welke(0);

%init sum p:Nat . (p==0) -> welke(p) % + sum p:Int . (p==0) -> welke(p);

It is undocumented how the type checker resolves such ambiguities.

jgroote commented 12 years ago

2011-11-24 17:26:16: @wiegerw commented

This is an example showing that these ambiguities lead to surprising results (supplied by Jeroen Ketema).

test3.mcrl2

act p : Nat;
act p : Int;

proc A(n : Nat, m : Int) = p(n).A(n, m) + p(m).A(n, m);

init A(0, 0);

script

act p : Nat;
act p : Int;

proc A(n : Nat, m : Int) = p(n).A(n, m) + p(m).A(n, m);

init A(0, 0);

output

[17:25:47.196 info]    LTSs are not strongly bisimilar
[17:25:47.204 info]    LTSs are not branching bisimilar

jgroote commented 12 years ago

2011-11-24 17:29:21: @wiegerw commented

(corrected copy paste error)

This is an example showing that these ambiguities lead to surprising results (supplied by Jeroen Ketema).

test3.mcrl2

act p : Nat;
act p : Int;

proc A(n : Nat, m : Int) = p(n).A(n, m) + p(m).A(n, m);

init A(0, 0);

script

mcrl22lps test3.mcrl2 test3.lps
lpspp test3.lps test4.mcrl2
mcrl22lps test4.mcrl2 test4.lps

lps2lts test3.lps test3.lts
lps2lts test4.lps test4.lts

ltscompare -ebisim test3.lts test4.lts
ltscompare -ebranching-bisim test3.lts test4.lts

output

[17:25:47.196 info]    LTSs are not strongly bisimilar
[17:25:47.204 info]    LTSs are not branching bisimilar

jgroote commented 12 years ago

2012-01-30 12:58:47: @jkeiren commented

As far as I can see, this issue can only occur in the case of the predefined numeric datatypes. In this case, observe that all ambiguities that occur in this way, may semantically be interpreted in the same way.

In user-defined cases, it is not allowed to define overloaded constructor/constants.

jgroote commented 12 years ago