units: Add factoring variable to limit simplifications

When factoring out units, we don't need to run through each
simplification in `expression::simplify`. We should also not lookup
names as symbols, but just let symbols as is.

Fixes: #988
Fixes: #976

Signed-off-by: Christophe de Dinechin <christophe@dinechin.org>

src/arithmetic.cc

@@ -1343,7 +1343,7 @@ algebraic_p arithmetic::evaluate(id          op,
         x = expression::make(op, x, y);
         if (x)
             if (expression_p expr = x->as<expression>())
-                if (Settings.AutoSimplify())
+                if (!unit::factoring && Settings.AutoSimplify())
                     x = expr->simplify();
         return x;
     }

src/expression.cc

@@ -1248,9 +1248,10 @@ algebraic_p expression::simplify_products() const
         if (inner->is_algebraic())
             return algebraic_p(inner);
 
-    // Save auto-simplify and set it
+    // Save auto-simplify and set it, and evaluate units normally
     settings::SaveAutoSimplify sas(true);
-    save<bool> save(unit::mode, false);
+    save<bool> smode(unit::mode, false);
+    save<bool> sexpr(unit::factoring, true);
 
     // Need a GC pointer since stack operations may move us
     expression_g eq   = this;

src/functions.cc

@@ -64,7 +64,7 @@ algebraic_p function::symbolic(id op, algebraic_r x)
     if (!x)
         return nullptr;
     expression_p result = expression::make(op, x);
-    if (result && Settings.AutoSimplify())
+    if (result && !unit::factoring && Settings.AutoSimplify())
         result = result->simplify();
     return result;
 }

src/symbol.cc

@@ -51,16 +51,19 @@ EVAL_BODY(symbol)
 //   Evaluate a symbol by looking it up
 // ----------------------------------------------------------------------------
 {
-    if (unit::mode)
-        if (unit_p u = unit::lookup(o))
-            if (rt.push(u))
-                return OK;
-    if (object_p found = directory::recall_all(o, false))
+    if (!unit::factoring)
     {
-        if (unit::ignore)
-            if (unit_p uval = found->as<unit>())
-                found = uval->value();
-        return program::run_program(found);
+        if (unit::mode)
+            if (unit_p u = unit::lookup(o))
+                if (rt.push(u))
+                    return OK;
+        if (object_p found = directory::recall_all(o, false))
+        {
+            if (unit::ignore)
+                if (unit_p uval = found->as<unit>())
+                    found = uval->value();
+            return program::run_program(found);
+        }
     }
     if (object_g eq = expression::make(o))
         if (rt.push(eq))

src/tests.cc

@@ -4140,7 +4140,7 @@ void tests::units_and_conversions()
         .test(SHIFT, KEY5, KEY4, KEY2, F2, F3).expect("42 km/h")
         .test(ADD).expect("101.54572 8 km/h");
     step("Unit parsing on command line")
-        .test(CLEAR, "12_km/s^2", ENTER).expect("12 km/s²");
+        .test(CLEAR, "12_km/s^2", ENTER).expect("12 km/s↑2");
     step("Parsing degrees as a unit")
         .test(CLEAR, "DEG", ENTER).noerror()
         .test("1∡90", ENTER).expect("1∡90°")
@@ -6904,7 +6904,7 @@ void tests::insertion_of_variables_constants_and_units()
         .expect("6.02213 67⁳²³ mol⁻¹");
     step("Programmatic equation lookup (text)")
         .test(CLEAR, "\"IdealGas\" LIBEQ", ENTER)
-        .expect("'(P Pa)·(V m³)=(n mol)·R·(T K)'");
+        .expect("'(P Pa)·(V m↑3)=(n mol)·R·(T K)'");
     step("Programmatic library lookup (text)")
         .test(CLEAR, "\"LibraryHelp\" XLIB", ENTER)
         .expect("\"To modify the library, edit the config/library.csv file\"");

src/unit.cc

@@ -256,6 +256,9 @@ HELP_BODY(unit)
 // This variable is true while evaluating a uexpr
 bool unit::mode = false;
 
+// This variable is true while factoring out a uexpr (limit simplifications)
+bool unit::factoring = false;
+
 // This variable is true to ignore units while solving an equation
 bool unit::ignore = false;
 

src/unit.h

@@ -62,6 +62,7 @@ struct unit : complex
     unit_p custom_cycle(symbol_r sym) const;
 
     static bool mode;           // Set to true to evaluate units
+    static bool factoring;      // Set to true when factoring out units
     static bool ignore;         // Set to true to drop units from variables
 
 public: