[Rafael-SOWNet]

Fixes #2227.

A statement in a numeric position, such as the argument of sin or a summand, has no value: evaluation leaves sin(True) and True + 2 as written. Each compiler disagreed with that, in its own way:

• FastExpression carries a statement as its truth value, so it took True as 1. sin(x > 1) at 2 was 0.8414709848078965, and max(x > 1, 0) was 1. This came with FastExpression compiles statements, provided and piecewise #2209 and is unreleased.
• The LINQ compiler threw KeyNotFoundException for sin(x > 1) and (x > 1)^2, from widening a bool to double. For max(x > 1, 0) it threw AngouriBugException, which asks for a bug report. Both are on 2.6.0.

StatementPositions.Check now runs in both compilers, after the membership rewrite and before anything is compiled. A statement-valued node is a statement, or a provided or piecewise over one. It may stand:

• at the root;
• as an operand of a connective;
• on both sides of an equality of statements;
• in an Iverson bracket;
• as a provided's or a piecewise's value or predicate;
• in a set or a quantifier.

Anywhere else it is refused with UncompilableNodeException, whose message points to iverson, the way to take a statement as a number.

	2.6.0	master	now
"sin(x > 1)".ToEntity().Compile("x").Call(2)	refused	(0.8414709848078965, 0)	refused
"sin(x > 1)".ToEntity().Compile<double, double>("x")	throws KeyNotFoundException	throws KeyNotFoundException	refused
"max(x > 1, 0)".ToEntity().Compile<double, double>("x")	throws AngouriBugException	throws AngouriBugException	refused

Tests: StatementInANumericPositionTest has 10 statements in numeric positions, refused by FastExpression and by LINQ over double and over Complex; all 10 fail without the check. It also has 8 places where a statement is taken, which compile as before. Full suite 18060/0, interactive trio, AOT smoke 73/0, all frameworks build.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.68%. Comparing base (595f523) to head (fbc2d11).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2229   +/-   ##
=======================================
  Coverage   86.68%   86.68%           
=======================================
  Files         309      310    +1     
  Lines       67660    67679   +19     
  Branches    19621    19627    +6     
=======================================
+ Hits        58648    58665   +17     
  Misses       4895     4895           
- Partials     4117     4119    +2     

Flag	Coverage Δ
cpp	37.77% <ø> (ø)
csharp	87.23% <100.00%> (+<0.01%)	⬆️
fsharp	32.97% <ø> (ø)
interactive	40.72% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...gouriMath/Functions/Compilation/IntoFE/Compiler.cs	85.33% <100.00%> (+0.30%)	⬆️
...Functions/Compilation/IntoLinq/IntoLinqCompiler.cs	96.87% <100.00%> (+0.04%)	⬆️
...riMath/Functions/Compilation/StatementPositions.cs	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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