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Allow inspect statements #738

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Allow inspect statements #738

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b639139
Allow inspect statements
ntrel Oct 7, 2023
d59e92b
Fix '= compound-statement' case
ntrel Oct 14, 2023
1dee1b3
Don't add `;` unless it was already there
ntrel Oct 18, 2023
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18 changes: 18 additions & 0 deletions regression-tests/pure2-inspect-statement.cpp2
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Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
v : std::any = ();

f: () -> int =
inspect v {
is 1 = return 1;
is int = { return 2; }
is _ = return 3;
}

main: () =
{
v = 1;
[[assert: f() == 1]]
v = 10;
[[assert: f() == 2]]
v = true;
[[assert: f() == 3]]
}
41 changes: 41 additions & 0 deletions regression-tests/test-results/pure2-inspect-statement.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,41 @@


//=== Cpp2 type declarations ====================================================


#include "cpp2util.h"



//=== Cpp2 type definitions and function declarations ===========================

extern std::any v;

[[nodiscard]] auto f() -> int;


#line 10 "pure2-inspect-statement.cpp2"
auto main() -> int;


//=== Cpp2 function definitions =================================================

std::any v {};

[[nodiscard]] auto f() -> int
{ auto&& _expr = v;
if (cpp2::is(_expr, 1)) return 1;
else if (cpp2::is<int>(_expr)) {return 2; }
else return 3;
}

auto main() -> int
{
v = 1;
cpp2::Default.expects(f() == 1, "");
v = 10;
cpp2::Default.expects(f() == 2, "");
v = true;
cpp2::Default.expects(f() == 3, "");
}

1 change: 1 addition & 0 deletions regression-tests/test-results/pure2-inspect-statement.cpp2.output
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@@ -0,0 +1 @@
pure2-inspect-statement.cpp2... ok (all Cpp2, passes safety checks)
17 changes: 8 additions & 9 deletions source/cppfront.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1943,15 +1943,15 @@ class cppfront
printer.emit_to_string(&statement);
emit(*alt->statement);
printer.emit_to_string();
// ... and jettison the final ; for an expression-statement
while (
!statement.empty()
&& (
statement.back() == ';'
|| isspace(statement.back())
)
)
// ... and jettison any final ; for an expression-statement
auto return_suffix = std::string{};
while (!statement.empty())
{
if (statement.back() == ';') {
return_suffix = ';'; // tack the ; back on in the alternative body
} else if (!isspace(statement.back())) {
break;
}
statement.pop_back();
}

Expand All @@ -1961,7 +1961,6 @@ class cppfront
// in an 'if constexpr' so that its type is ignored for mismatches with
// the inspect-expression's type
auto return_prefix = std::string{};
auto return_suffix = std::string{";"}; // use this to tack the ; back on in the alternative body
if (is_expression) {
return_prefix = "{ if constexpr( requires{" + statement + ";} ) if constexpr( std::is_convertible_v<CPP2_TYPEOF((" + statement + "))," + result_type + "> ) return ";
return_suffix += " }";
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8 changes: 0 additions & 8 deletions source/parse.h
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Original file line number Diff line number Diff line change
Expand Up @@ -6770,14 +6770,6 @@ class parser
return {};
}

if (!is_expression) {
errors.emplace_back(
curr().position(),
"(temporary alpha limitation) cppfront is still learning 'inspect' - only inspect expressions are currently supported"
);
return {};
}

Comment on lines -6773 to -6780
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Is this the correct implementation?
I don't think there's code to lower inspect statements.
What happens with this code?

main: () = {
  inspect 0 {
    is 0 = std::cout << "0\n";
    is _ = std::cout << "?\n";
  }
}

In the test case, the inspect is actually the expression of an expression-statement.
Could it be that is_expression should have been true in this case?

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@ntrel ntrel Oct 9, 2023 •
edited
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Oh that doesn't work. So yes it seems the test case is doing return inspect v {.

It does work actually!

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I don't think there's code to lower inspect statements.

There is, in emit(inspect_expression_node, bool). If is_expression is false, the lambda parameters and inline call are not emitted, but the braces still are emitted. So it just generates a block. You can see it in the diff here.

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While your example does work, the following does not:

  inspect 0 {
    is 0 = { std::cout << "0\n"; }
    is _ = std::cout << "?\n";
  }

The Cpp1 code has a semi-colon before the else clause, causing an error. I'll try to fix it.

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Maybe you should scope your PR
to treating inspect as an expression rather than as a statement
when it is a declaration's statement.

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Now pushed a simple fix.

auto n = std::make_unique<inspect_expression_node>();
n->identifier = &curr();
next();
Expand Down