Merge pull request #511 from HigherOrderCO/427-request-else-if-chains

#427 else if chains

Cargo.toml

@@ -2,7 +2,7 @@
 name = "bend-lang"
 description = "A high-level, massively parallel programming language"
 license = "Apache-2.0"
-version = "0.2.23"
+version = "0.2.24"
 edition = "2021"
 rust-version = "1.74"
 exclude = ["tests/snapshots/"]

cspell.json

@@ -32,6 +32,8 @@
     "dref",
     "dups",
     "effectful",
+    "elif",
+    "elifs",
     "foldl",
     "hasher",
     "hexdigit",
@@ -120,10 +122,7 @@
     "walkdir",
     "wopts"
   ],
-  "files": [
-    "**/*.rs",
-    "**/*.md"
-  ],
+  "files": ["**/*.rs", "**/*.md"],
   "ignoreRegExpList": [
     "HexValues",
     "/λ/g",

docs/syntax.md

@@ -193,6 +193,20 @@ A branching statement where `else` is mandatory.
 
 The condition must return a `u24` number, where 0 will run the `else` branch and any other value will return the first one.
 
+It is possible to make if-chains using `elif`:
+
+```python
+if condition1:
+  return 0
+elif condition2:
+  return 1
+elif condition3:
+  return 2
+else:
+  return 3
+```
+The conditions are evaluated in order, one by one, stopping at the first successful case.
+
 ### Switch
 
 ```python

src/imp/parser.rs

@@ -532,13 +532,35 @@ impl<'a> PyParser<'a> {
     if nxt_indent != *indent {
       return self.expected_indent(*indent, nxt_indent);
     }
+    let mut elifs = Vec::new();
+    while self.try_parse_keyword("elif") {
+      let cond = self.parse_expr(true)?;
+      self.skip_trivia_inline();
+      self.consume_exactly(":")?;
+      indent.enter_level();
+      self.consume_indent_exactly(*indent)?;
+      let (then, nxt_indent) = self.parse_statement(indent)?;
+      indent.exit_level();
+
+      if nxt_indent != *indent {
+        return self.expected_indent(*indent, nxt_indent);
+      }
+      elifs.push((cond, then));
+    }
     self.parse_keyword("else")?;
     self.skip_trivia_inline();
     self.consume_exactly(":")?;
     indent.enter_level();
 
     self.consume_indent_exactly(*indent)?;
     let (otherwise, nxt_indent) = self.parse_statement(indent)?;
+    let otherwise = elifs.into_iter().fold(otherwise, |acc, (cond, then)| Stmt::If {
+      cond: Box::new(cond),
+      then: Box::new(then),
+      otherwise: Box::new(acc),
+      nxt: None,
+    });
+
     indent.exit_level();
     if nxt_indent == *indent {
       let (nxt, nxt_indent) = self.parse_statement(indent)?;

tests/golden_tests/compile_file/elif.bend

@@ -0,0 +1,16 @@
+def main:
+  cond1 = 1 == 2
+  cond2 = 2 < 1
+  cond3 = 3 > 2
+  cond4 = 2 == 2
+  if cond1:
+    res = 1
+  elif cond2:
+    res = 2
+  elif cond3:
+    res = 3
+  elif cond4:
+    res = 4
+  else:
+    res = 0
+  return res

tests/golden_tests/compile_file/elif_no_else.bend

@@ -0,0 +1,5 @@
+def main:
+  if 1 == 1:
+    return 0
+  elif 2 == 2:
+    return 1

tests/snapshots/compile_file__elif.bend.snap

@@ -0,0 +1,18 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/compile_file/elif.bend
+---
+@main = d
+  & @main__C3 ~ (a (b (c d)))
+  & $(1 a) ~ [<2]
+  & $(2 b) ~ [>3]
+  & $(2 c) ~ [=2]
+
+@main__C0 = (?((0 (* 2)) a) a)
+
+@main__C1 = (a (?((@main__C0 (* (* 3))) (a b)) b))
+
+@main__C2 = (a (b (?((@main__C1 (* (* (* 4)))) (a (b c))) c)))
+
+@main__C3 = a
+  & $(2 ?((@main__C2 (* (* (* (* 1))))) a)) ~ [=1]

tests/snapshots/compile_file__elif_no_else.bend.snap

@@ -0,0 +1,8 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/compile_file/elif_no_else.bend
+---
+Errors:
+In tests/golden_tests/compile_file/elif_no_else.bend :
+Indentation error. Expected 2 spaces, got end-of-input.
+  6 |