🐐 String interpolation

tests.py

@@ -12,9 +12,9 @@ from fractions import Fraction
 from centvrion.ast_nodes import (
   ArrayIndex, Bool, BinOp, BuiltIn, DataArray, DataRangeArray, Defini,
   Continva, Designa, DesignaDestructure, DesignaIndex, DumStatement, Erumpe,
-  ExpressionStatement, ID, Invoca, ModuleCall, Nullus, Numeral, PerStatement,
-  Program, Redi, SiStatement, String, UnaryMinus, UnaryNot,
-  Fractio, frac_to_fraction, fraction_to_frac,
+  ExpressionStatement, ID, InterpolatedString, Invoca, ModuleCall, Nullus,
+  Numeral, PerStatement, Program, Redi, SiStatement, String, UnaryMinus,
+  UnaryNot, Fractio, frac_to_fraction, fraction_to_frac,
   num_to_int, int_to_num, make_string,
 )
 from centvrion.compiler.emitter import compile_program
@@ -881,6 +881,99 @@ class TestStringConcat(unittest.TestCase):
     run_test(self, source, nodes, value)
 
 
+# --- String interpolation ---
+
+interpolation_tests = [
+  # basic variable interpolation
+  ('DESIGNA nomen VT "Marcus"\n"Salve, {nomen}!"',
+    Program([], [
+      Designa(ID("nomen"), String("Marcus")),
+      ExpressionStatement(InterpolatedString([String("Salve, "), ID("nomen"), String("!")]))
+    ]), ValStr("Salve, Marcus!")),
+  # arithmetic expression inside interpolation
+  ('DESIGNA x VT III\n"Sum: {x + II}"',
+    Program([], [
+      Designa(ID("x"), Numeral("III")),
+      ExpressionStatement(InterpolatedString([String("Sum: "), BinOp(ID("x"), Numeral("II"), "SYMBOL_PLUS")]))
+    ]), ValStr("Sum: V")),
+  # multiple interpolations
+  ('DESIGNA a VT I\nDESIGNA b VT II\n"{a} + {b} = {a + b}"',
+    Program([], [
+      Designa(ID("a"), Numeral("I")),
+      Designa(ID("b"), Numeral("II")),
+      ExpressionStatement(InterpolatedString([
+        ID("a"), String(" + "), ID("b"), String(" = "),
+        BinOp(ID("a"), ID("b"), "SYMBOL_PLUS"),
+      ]))
+    ]), ValStr("I + II = III")),
+  # escaped braces become literal
+  ('"use {{braces}}"',
+    Program([], [ExpressionStatement(String("use {braces}"))]),
+    ValStr("use {braces}")),
+  # single-quoted strings ignore braces
+  ("'hello {world}'",
+    Program([], [ExpressionStatement(String("hello {world}"))]),
+    ValStr("hello {world}")),
+  # integer coercion
+  ('DESIGNA n VT V\n"n is {n}"',
+    Program([], [
+      Designa(ID("n"), Numeral("V")),
+      ExpressionStatement(InterpolatedString([String("n is "), ID("n")]))
+    ]), ValStr("n is V")),
+  # boolean coercion
+  ('DESIGNA b VT VERITAS\n"value: {b}"',
+    Program([], [
+      Designa(ID("b"), Bool(True)),
+      ExpressionStatement(InterpolatedString([String("value: "), ID("b")]))
+    ]), ValStr("value: VERITAS")),
+  # NVLLVS coercion
+  ('"value: {NVLLVS}"',
+    Program([], [
+      ExpressionStatement(InterpolatedString([String("value: "), Nullus()]))
+    ]), ValStr("value: NVLLVS")),
+  # expression-only string (no literal parts around it)
+  ('DESIGNA x VT "hi"\n"{x}"',
+    Program([], [
+      Designa(ID("x"), String("hi")),
+      ExpressionStatement(InterpolatedString([ID("x")]))
+    ]), ValStr("hi")),
+  # adjacent interpolations
+  ('DESIGNA a VT "x"\nDESIGNA b VT "y"\n"{a}{b}"',
+    Program([], [
+      Designa(ID("a"), String("x")),
+      Designa(ID("b"), String("y")),
+      ExpressionStatement(InterpolatedString([ID("a"), ID("b")]))
+    ]), ValStr("xy")),
+  # function call inside interpolation
+  ("DEFINI f () VT {\nREDI (V)\n}\n\"result: {INVOCA f()}\"",
+    Program([], [
+      Defini(ID("f"), [], [Redi([Numeral("V")])]),
+      ExpressionStatement(InterpolatedString([String("result: "), Invoca(ID("f"), [])]))
+    ]), ValStr("result: V")),
+  # single-quoted string inside interpolation
+  ("DESIGNA x VT 'hello'\n\"{x & '!'}\"",
+    Program([], [
+      Designa(ID("x"), String("hello")),
+      ExpressionStatement(InterpolatedString([BinOp(ID("x"), String("!"), "SYMBOL_AMPERSAND")]))
+    ]), ValStr("hello!")),
+  # plain double-quoted string (no braces) still works
+  ('"hello world"',
+    Program([], [ExpressionStatement(String("hello world"))]),
+    ValStr("hello world")),
+  # interpolation in DICE output
+  ('DESIGNA name VT "Roma"\nDICE("Salve, {name}!")',
+    Program([], [
+      Designa(ID("name"), String("Roma")),
+      ExpressionStatement(BuiltIn("DICE", [InterpolatedString([String("Salve, "), ID("name"), String("!")])]))
+    ]), ValStr("Salve, Roma!"), "Salve, Roma!\n"),
+]
+
+class TestInterpolation(unittest.TestCase):
+  @parameterized.expand(interpolation_tests)
+  def test_interpolation(self, source, nodes, value, output=""):
+    run_test(self, source, nodes, value, output)
+
+
 # --- Comparison operators ---
 
 comparison_tests = [