Allow x, y: int syntax for declaring local variables (#540)

doc/tutorial.md

@@ -308,17 +308,16 @@ def get_point(x: int*, y: int*) -> None:
     *y = 456
 
 def main() -> int:
-    x: int
-    y: int
+    x, y: int
     get_point(&x, &y)
     printf("The point is (%d,%d)\n", x, y)  # Output: The point is (123,456)
     return 0
 ```
 
-Here `x: int` creates an integer variable `x` without assigning a value to it.
-This means that we leave 4 bytes of the computer's memory unused for now.
+Here `x, y: int` creates two integer variables without assigning values to them.
+This means that we leave 8 bytes (4 bytes for both) of the computer's memory unused for now.
 We then pass the location of that memory to `get_point()`,
-so that it can write to that memory, i.e. set the value of the `x` variable.
+so that it can write to that memory, i.e. set the values of the `x` and `y` variables.
 
 Instead of pointers, you could also use an `int[2]` array to return the two values:
 
@@ -366,15 +365,14 @@ def get_point(x: int*, y: int*) -> None:
     *y = 456
 
 def main() -> int:
-    x: int
-    y: int
+    x, y: int
     get_point(&x, &y)
     printf("The point is (%d,%d)\n", x, y)  # Output: The point is (123,456)
     return 0
 ```
 
-Here `x: int` creates a variable of type `int` without assigning a value to it.
-If you try to use the value of `x` before it is set,
+Here `x, y: int` creates two variables of type `int` without assigning values to them.
+If you try to use the value of `x` or `y` before they are set,
 you will most likely get a compiler warning together with a random garbage value when the program runs.
 For example, if I delete the `get_point(&x, &y)` line, I get:
 

examples/aoc2023/day03/part2.jou

@@ -55,8 +55,7 @@ def find_adjacent_numbers(input: byte*, p: byte*) -> int[10]:
         for dx = -1; dx <= 1; dx++:
             neighbor = &p[dx + line_size*dy]
             if input <= neighbor and neighbor < &input[strlen(input)] and is_ascii_digit(*neighbor):
-                start: byte*
-                end: byte*
+                start, end: byte*
                 find_whole_number(input, neighbor, &start, &end)
                 if start != last_start or end != last_end:
                     last_start = start

examples/aoc2023/day05/part1.jou

@@ -9,9 +9,7 @@ class Map:
     ntriples: int
 
     def add_triple(self, s: byte*) -> None:
-        a: long
-        b: long
-        c: long
+        a, b, c: long
         assert sscanf(s, "%lld %lld %lld", &a, &b, &c) == 3
 
         assert self->ntriples < sizeof(self->triples)/sizeof(self->triples[0])

examples/aoc2023/day05/part2.jou

@@ -42,9 +42,7 @@ class Map:
     ntriples: int
 
     def add_triple(self, s: byte*) -> None:
-        a: long
-        b: long
-        c: long
+        a, b, c: long
         assert sscanf(s, "%lld %lld %lld", &a, &b, &c) == 3
 
         assert self->ntriples < sizeof(self->triples)/sizeof(self->triples[0])

examples/aoc2023/day24/part1.jou

@@ -164,12 +164,7 @@ def main() -> int:
 
     r: Ray
 
-    x: long
-    y: long
-    z: long
-    dx: long
-    dy: long
-    dz: long
+    x, y, z, dx, dy, dz: long
     while fscanf(f, "%lld, %lld, %lld @ %lld, %lld, %lld\n", &x, &y, &z, &dx, &dy, &dz) == 6:
         assert nrays < sizeof(rays)/sizeof(rays[0])
         rays[nrays++] = Ray{start = [x,y], dir = [dx,dy]}

examples/aoc2023/day24/part2.jou

@@ -174,12 +174,7 @@ def read_input(N: int) -> MovingPoint*:
 
     result: MovingPoint* = malloc(N * sizeof(result[0]))
     for i = 0; i < N; i++:
-        x: long
-        y: long
-        z: long
-        dx: long
-        dy: long
-        dz: long
+        x, y, z, dx, dy, dz: long
         assert fscanf(f, "%lld, %lld, %lld @ %lld, %lld, %lld\n", &x, &y, &z, &dx, &dy, &dz) == 6
         result[i] = MovingPoint{start = [x,y,z], speed = [dx,dy,dz]}
 

examples/aoc2024/day01/part1.jou

@@ -19,8 +19,7 @@ def main() -> int:
     f = fopen("sampleinput.txt", "r")
     assert f != NULL
 
-    left_column: int[2000]
-    right_column: int[2000]
+    left_column, right_column: int[2000]
     n = 0
     while fscanf(f, "%d %d", &left_column[n], &right_column[n]) == 2:
         n++

examples/aoc2024/day13/part1.jou

@@ -33,13 +33,7 @@ def main() -> int:
     assert f != NULL
 
     total_price = 0
-
-    ax: int
-    ay: int
-    bx: int
-    by: int
-    px: int
-    py: int
+    ax, ay, bx, by, px, py: int
 
     while True:
         ret = fscanf(f, "Button A: X+%d, Y+%d\n", &ax, &ay)

examples/aoc2024/day13/part2.jou

@@ -181,13 +181,7 @@ def main() -> int:
     assert f != NULL
 
     total_price = 0L
-
-    ax: long
-    ay: long
-    bx: long
-    by: long
-    px: long
-    py: long
+    ax, ay, bx, by, px, py: long
 
     while True:
         ret = fscanf(f, "Button A: X+%lld, Y+%lld\n", &ax, &ay)

examples/aoc2024/day14/part1.jou

@@ -52,10 +52,7 @@ def main() -> int:
 
     qcounts: int[5] = [0, 0, 0, 0, 0]
 
-    px: int
-    py: int
-    vx: int
-    vy: int
+    px, py, vx, vy: int
     while fscanf(f, "p=%d,%d v=%d,%d\n", &px, &py, &vx, &vy) == 4:
         x = (px + 100*vx) % width
         y = (py + 100*vy) % height

examples/aoc2024/day14/part2.jou

@@ -40,10 +40,7 @@ def main() -> int:
     assert robots != NULL
     nrobots = 0
 
-    px: int
-    py: int
-    vx: int
-    vy: int
+    px, py, vx, vy: int
     while fscanf(f, "p=%d,%d v=%d,%d\n", &px, &py, &vx, &vy) == 4:
         assert nrobots < max_robots
         robots[nrobots++] = Robot{

examples/aoc2024/day18/part2.jou

@@ -32,8 +32,7 @@ def main() -> int:
     assert f != NULL
 
     memset(&grid, '.', sizeof(grid))
-    x_in: int
-    y_in: int
+    x_in, y_in: int
     while fscanf(f, "%d,%d\n", &x_in, &y_in) == 2:
         assert 0 <= x_in and x_in < size
         assert 0 <= y_in and y_in < size

self_hosted/parser.jou

@@ -842,6 +842,44 @@ class Parser:
             body = self->parse_body(),
         }
 
+    # Parses the "x: int" part of "x, y, z: int", leaving "y, z: int" to be parsed later.
+    def parse_first_of_multiple_local_var_declares(self) -> AstNameTypeValue:
+        assert self->tokens->kind == TokenKind::Name
+
+        ntv = AstNameTypeValue{
+            name = self->tokens->short_string,
+            name_location = self->tokens->location,
+        }
+
+        # Take a backup of the parser where first variable name and its comma are consumed.
+        save_state = *self
+        save_state.tokens = &save_state.tokens[2]
+
+        # Skip variables and commas so we can parse the type that comes after it
+        self->tokens++
+        while self->tokens->is_operator(",") and self->tokens[1].kind == TokenKind::Name:
+            self->tokens = &self->tokens[2]
+
+        # Error for "x, y = 0"
+        if self->tokens->is_operator("="):
+            fail(self->tokens->location, "only one variable can be assigned at a time")
+
+        if self->tokens->is_operator("="):
+            fail(self->tokens->location, "only one variable can be assigned at a time")
+
+        if not self->tokens->is_operator(":"):
+            self->tokens->fail_expected_got("':' and a type after it (example: \"foo, bar: int\")")
+        self->tokens++
+
+        ntv.type = self->parse_type()
+
+        # Error for "x, y: int = 0"
+        if self->tokens->is_operator("="):
+            fail(self->tokens->location, "only one variable can be assigned at a time")
+
+        *self = save_state
+        return ntv
+
     def parse_statement(self) -> AstStatement:
         if self->tokens->is_keyword("import"):
             fail(self->tokens->location, "imports must be in the beginning of the file")
@@ -924,6 +962,17 @@ class Parser:
                 while_loop = self->parse_while_loop(),
             }
 
+        if (
+            self->tokens[0].kind == TokenKind::Name
+            and self->tokens[1].is_operator(",")
+            and self->tokens[2].kind == TokenKind::Name
+        ):
+            return AstStatement{
+                location = self->tokens->location,
+                kind = AstStatementKind::DeclareLocalVar,
+                var_declaration = self->parse_first_of_multiple_local_var_declares(),
+            }
+
         result = self->parse_oneline_statement()
         self->eat_newline()
         return result

src/parse.c

@@ -957,6 +957,42 @@ static AstEnumDef parse_enumdef(ParserState *ps)
     return result;
 }
 
+// Parses the "x: int" part of "x, y, z: int", leaving "y, z: int" to be parsed later.
+static AstNameTypeValue parse_first_of_multiple_local_var_declares(ParserState *ps)
+{
+    assert(ps->tokens->type == TOKEN_NAME);
+    assert(is_operator(&ps->tokens[1], ","));
+
+    AstNameTypeValue ntv = { .name_location = ps->tokens->location, .value = NULL };
+    safe_strcpy(ntv.name, ps->tokens->data.name);
+
+    // Take a backup of the parser where first variable name and its comma are consumed.
+    ParserState savestate = *ps;
+    savestate.tokens += 2;
+
+    // Skip variables and commas so we can parse the type that comes after it
+    ps->tokens++;
+    while (is_operator(ps->tokens, ",") && ps->tokens[1].type == TOKEN_NAME)
+        ps->tokens += 2;
+
+    // Error for "x, y = 0"
+    if (is_operator(ps->tokens, "="))
+        fail(ps->tokens->location, "only one variable can be assigned at a time");
+
+    if (!is_operator(ps->tokens, ":"))
+        fail_with_parse_error(ps->tokens, "':' and a type after it (example: \"foo, bar: int\")");
+    ps->tokens++;
+
+    ntv.type = parse_type(ps);
+
+    // Error for "x, y: int = 0"
+    if (is_operator(ps->tokens, "="))
+        fail(ps->tokens->location, "only one variable can be assigned at a time");
+
+    *ps = savestate;
+    return ntv;
+}
+
 static AstStatement parse_statement(ParserState *ps)
 {
     AstStatement result = { .location = ps->tokens->location };
@@ -1031,6 +1067,9 @@ static AstStatement parse_statement(ParserState *ps)
         ps->tokens++;
         *result.data.forloop.incr = parse_oneline_statement(ps);
         result.data.forloop.body = parse_body(ps);
+    } else if (ps->tokens->type == TOKEN_NAME && is_operator(&ps->tokens[1], ",") && ps->tokens[2].type == TOKEN_NAME) {
+        result.kind = AST_STMT_DECLARE_LOCAL_VAR;
+        result.data.vardecl = parse_first_of_multiple_local_var_declares(ps);
     } else {
         result = parse_oneline_statement(ps);
         eat_newline(ps);

tests/should_succeed/sscanf.jou

@@ -2,8 +2,7 @@ import "stdlib/io.jou"
 import "stdlib/str.jou"
 
 def calculate_sum(string: byte*) -> int:
-    x: int
-    y: int
+    x, y: int
     sscanf(string, "%d + %d", &x, &y)
     return x + y
 

tests/syntax_error/double_assignment_comma_typed.jou

@@ -0,0 +1,2 @@
+def foo() -> None:
+    x, y: int = 7  # Error: only one variable can be assigned at a time

tests/syntax_error/double_assignment_comma_untyped.jou

@@ -0,0 +1,4 @@
+def foo() -> None:
+    # Python's unpack syntax is not supported in Jou.
+    # If you think it should be supported, note that it conflicts with "x, y: int" syntax (see #536).
+    x, y = 0  # Error: only one variable can be assigned at a time

tests/syntax_error/local_var_comma.jou

@@ -0,0 +1,2 @@
+def main() -> int:
+    x, = 0  # Error: not a valid statement

tests/syntax_error/local_vars_comma.jou

@@ -0,0 +1,2 @@
+def main() -> int:
+    x, y, = 0  # Error: expected ':' and a type after it (example: "foo, bar: int"), got ','

tests/syntax_error/local_vars_comma_assign.jou

@@ -0,0 +1,2 @@
+def main() -> int:
+    x, y,  # Error: expected ':' and a type after it (example: "foo, bar: int"), got ','

tests/syntax_error/python_style_unpack.jou

@@ -0,0 +1,2 @@
+def main() -> int:
+    x, y = "hi"  # Error: only one variable can be assigned at a time