Add IFS function (like Excel)

README.md

@@ -98,6 +98,7 @@ The following are changes from the original TinyExpr C library:
   - `fact`: alias for `fac()`, like the *Excel* function.
   - `false`: returns `false` (i.e., `0`) in a boolean expression.
   - `if`: if a value is true (i.e., non-zero), then returns the second argument; otherwise, returns the third argument.
+  - `ifs`: checks up to three conditions, returning the value corresponding to the first met condition.
   - `max`: returns the maximum of a range of values (accepts 1-7 arguments).
   - `min`: returns the minimum of a range of values (accepts 1-7 arguments).
   - `mod`: returns remainder from a division.

docs/manual/09-EndUserUsage.Rmd

@@ -38,6 +38,21 @@ IF(AND(smartMeter1.power > 1,900, sensor1.temperature < 52), TRUE,
 ```
 :::
 
+::: {.minipage data-latex="{\textwidth}"}
+The same can be accomplished using the `IFS()` function:
+
+```cpp
+IFS(AND(smartMeter1.power > 1900, sensor1.temperature < 52), TRUE,
+    // First logical check failed, so now check another scenarios
+    // and return false either meets our criteria.
+    AND(smartMeter1.power < 0), FALSE,
+    AND(smartMeter1.power < 300, sensor1.temperature > 55), FALSE)
+
+    // NaN is returned if no conditions were met and we are
+    // in an unknown state.
+```
+:::
+
 ::: {.notesection data-latex=""}
 Expressions can optionally begin with an `=`, the same as spreadsheet programs. For example: \
 

docs/manual/11-Functions.Rmd

@@ -59,6 +59,7 @@ Table: Statistical Functions\index{functions!statistical}
 | :-- | :-- |
 | AND(Value1, Value2, ...) | Returns true if all conditions are true. |
 | IF(Condition, ValueIfTrue, ValueIfFalse) | If *Condition* is true (non-zero), then *ValueIfTrue* is returned; otherwise, *ValueIfFalse* is returned.<br>\linebreak Note that multiple `IF` commands can be nested to create a "case" statement\index{case statements}. |
+| IFS(Condition1, Value1, Condition2, Value2, ...) | Checks up to three conditions, returning the value corresponding to the first met condition.<br>\linebreak This is shorthand for multiple nested `IF` commands, providing better readability. Will accept 1–3 condition/value pairs.<br>\linebreak NaN will be returned if all conditions are false. |
 | NOT(Value) | Returns the logical negation of *Value.* |
 | OR(Value1, Value2, ...) | Returns true if any condition is true. |
 

tests/tetests.cpp

@@ -358,6 +358,26 @@ TEST_CASE("Main tests", "[main]")
         {
         CHECK(tep.evaluate("if(1, 9, 7)") == 9);
         CHECK(tep.evaluate("if(0, 9, 7)") == 7);
+        CHECK(tep.evaluate("if(0.000001 /* non-zero means true */, 9, 7)") == 9);
+
+        // no evaluation statement returns NaN
+        CHECK(std::isnan(tep.evaluate("IFS()")));
+        CHECK(std::isnan(tep.evaluate("IFS(0, 9)")));
+        CHECK(std::isnan(tep.evaluate("IFS(0.000, 9)")));
+        CHECK(std::isnan(tep.evaluate("IFS(FALSE, 9)")));
+        CHECK(tep.evaluate("IFS(true, 9, 0.0, 7, 1, 5)") == 9);
+        CHECK(tep.evaluate("IFS(FALSE, 9, TRUE, 7)") == 7);
+        CHECK(tep.evaluate("IFS(FALSE, 9, 0.0, 7, 1, 5)") == 5);
+        // complex expressions
+        CHECK(tep.evaluate("IFS(9 > 1, 9, 0.0, 7, 1, 5)") == 9);
+        CHECK(tep.evaluate("IFS(9 > 10, 9, 6 > 9, 6, AND(1 > 0, 1 > -1), 1)") == 1);
+        // all three expressions are false, so returns NaN
+        CHECK(std::isnan(tep.evaluate("IFS(false, 9, false, 7, false, 5)")));
+        // not enough args, so NaN is the default value for the last expression
+        CHECK(std::isnan(tep.evaluate("IFS(FALSE, 9, 0.0, 7, 1)")));
+        // NaN "condition" returns NaN
+        CHECK(std::isnan(tep.evaluate("IFS(NAN, 9)")));
+
         CHECK(tep.evaluate("and(0.0, 5)") == 0);
         CHECK(tep.evaluate("and(0.0, 0)") == 0);
         CHECK(tep.evaluate("AND(-1, 5)") == 1);

tinyexpr.cpp

@@ -468,6 +468,16 @@ static double _or_variadic(double v1, double v2, double v3, double v4,
 constexpr static double _if(double a, double b, double c) noexcept
     { return (a != 0.0) ? b : c; }
 [[nodiscard]]
+constexpr static double _ifs(double if1, double if1True,
+                             double if2, double if2True,
+                             double if3, double if3True) noexcept
+    {
+    return (!std::isnan(if1) && if1 != 0.0) ? if1True :
+        (!std::isnan(if2) && if2 != 0.0) ? if2True :
+        (!std::isnan(if3) && if3 != 0.0) ? if3True :
+        te_parser::te_nan;
+    }
+[[nodiscard]]
 constexpr static double _false_value() noexcept
     { return 0; }
 [[nodiscard]]
@@ -592,6 +602,7 @@ const std::set<te_variable> te_parser::m_functions = {
     {"false", static_cast<te_fun0>(_false_value), TE_PURE},
     {"floor", static_cast<te_fun1>(_floor), TE_PURE},
     {"if", static_cast<te_fun3>(_if), TE_PURE},
+    {"ifs", static_cast<te_fun6>(_ifs), static_cast<te_variable_flags>(TE_PURE|TE_VARIADIC)},
     {"ln", static_cast<te_fun1>(_log), TE_PURE},
     {"log10", static_cast<te_fun1>(_log10), TE_PURE},
     {"max", static_cast<te_fun7>(_max), static_cast<te_variable_flags>(TE_PURE|TE_VARIADIC)},