Feat: UI / UX

crates/forth/src/compiler.rs

@@ -160,6 +160,12 @@ fn compile(tokens: &[Token], dict: &Dictionary) -> Result<Vec<Op>, String> {
                         ops.push(Op::Branch(else_ops.len()));
                         ops.extend(else_ops);
                     }
+                } else if word == "case" {
+                    let (case_ops, consumed) = compile_case(&tokens[i + 1..], dict)?;
+                    i += consumed;
+                    ops.extend(case_ops);
+                } else if word == "of" || word == "endof" || word == "endcase" {
+                    return Err(format!("unexpected '{word}'"));
                 } else if !compile_word(word, Some(*span), &mut ops, dict) {
                     return Err(format!("unknown word: {word}"));
                 }
@@ -300,3 +306,69 @@ fn compile_if(
 
     Ok((then_ops, else_ops, then_pos + 1, then_span, else_span))
 }
+
+fn compile_case(tokens: &[Token], dict: &Dictionary) -> Result<(Vec<Op>, usize), String> {
+    let mut depth = 1;
+    let mut endcase_pos = None;
+    let mut clauses: Vec<(usize, usize)> = Vec::new();
+    let mut last_of = None;
+
+    for (i, tok) in tokens.iter().enumerate() {
+        if let Token::Word(w, _) = tok {
+            match w.as_str() {
+                "case" => depth += 1,
+                "endcase" => {
+                    depth -= 1;
+                    if depth == 0 {
+                        endcase_pos = Some(i);
+                        break;
+                    }
+                }
+                "of" if depth == 1 => last_of = Some(i),
+                "endof" if depth == 1 => {
+                    let of_pos = last_of.ok_or("'endof' without matching 'of'")?;
+                    clauses.push((of_pos, i));
+                    last_of = None;
+                }
+                _ => {}
+            }
+        }
+    }
+
+    let endcase_pos = endcase_pos.ok_or("missing 'endcase'")?;
+
+    let mut ops = Vec::new();
+    let mut branch_fixups: Vec<usize> = Vec::new();
+    let mut clause_start = 0;
+
+    for &(of_pos, endof_pos) in &clauses {
+        let test_ops = compile(&tokens[clause_start..of_pos], dict)?;
+        let body_ops = compile(&tokens[of_pos + 1..endof_pos], dict)?;
+
+        ops.extend(test_ops);
+        ops.push(Op::Over);
+        ops.push(Op::Eq);
+        ops.push(Op::BranchIfZero(body_ops.len() + 2, None, None));
+        ops.push(Op::Drop);
+        ops.extend(body_ops);
+        branch_fixups.push(ops.len());
+        ops.push(Op::Branch(0));
+
+        clause_start = endof_pos + 1;
+    }
+
+    let default_tokens = &tokens[clause_start..endcase_pos];
+    if !default_tokens.is_empty() {
+        let default_ops = compile(default_tokens, dict)?;
+        ops.extend(default_ops);
+    }
+
+    ops.push(Op::Drop);
+
+    let end = ops.len();
+    for pos in branch_fixups {
+        ops[pos] = Op::Branch(end - pos - 1);
+    }
+
+    Ok((ops, endcase_pos + 1))
+}