From fbc75bca57a3f66006468fb1a8f3988cdc8227d2 Mon Sep 17 00:00:00 2001
From: mryouse
Date: Wed, 7 Jun 2023 22:52:09 -0400
Subject: initial commit of branch

---
 compiler.d | 38 ++++++++++++++++++++++++++++++++++++++
 parser.d   | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/compiler.d b/compiler.d
index 675ec4c..8cb65ee 100644
--- a/compiler.d
+++ b/compiler.d
@@ -83,6 +83,41 @@ class Compiler {
         }
     }
 
+    void compileBranch(Form form) {
+
+        Branch branch = cast(Branch)form;
+
+        Cons clause;
+        int[] endJumps;
+        int currentJump;
+        foreach (Form cl ; branch.clauses) {
+            // resolve the condition
+            clause = cast(Cons)cl;
+            this.resolve(clause.head);
+            this.func.chunk.writeOp(OpCode.OP_TYPE_CHECK_BOOLEAN, clause.line);
+
+            // write a jump spot and pop
+            currentJump = this.jump(OpCode.OP_JUMP_IF_FALSE);
+            this.func.chunk.writeOp(OpCode.OP_POP, clause.line);
+
+            // resolve the result of the condition (only executes if true)
+            foreach (Form f ; clause.tail) {
+                this.resolve(f);
+            }
+
+            // jump to the end (if we got here)
+            endJumps ~= this.jump(OpCode.OP_JUMP);
+
+            // this is where we jump to if the condition was false
+            this.patchJump(currentJump);
+        }
+
+        // patch all the end jumps
+        foreach (int jmp; endJumps) {
+            this.patchJump(jmp);
+        }
+    }
+
     void compileIf(Form form) {
         If if_ = cast(If)form;
 
@@ -908,6 +943,9 @@ class Compiler {
             case FormType.IF:
                 this.compileIf(form);
                 break;
+            case FormType.BRANCH:
+                this.compileBranch(form);
+                break;
             case FormType.AND:
                 this.compileAnd(form);
                 break;
diff --git a/parser.d b/parser.d
index 004e1fb..0b31be8 100644
--- a/parser.d
+++ b/parser.d
@@ -17,6 +17,7 @@ enum FormType {
     DEF,
     BLOCK,
     IF,
+    BRANCH,
     AND,
     OR,
 
@@ -157,6 +158,20 @@ class If : Form {
 
 }
 
+class Branch : Form {
+
+    Form[] clauses;
+
+    this(int line) {
+        this.line = line;
+        this.type = FormType.BRANCH;
+    }
+
+    void addClause(Form clause) {
+        this.clauses ~= clause;
+    }
+}
+
 class And : Form {
 
     Form[] clauses;
@@ -605,6 +620,27 @@ class Parser {
         return if_;
     }
 
+    Form parseBranch() {
+        Branch branch = new Branch(-1);
+        Form f;
+        char next;
+        while(peekable()) {
+            next = peek();
+            if (next == ')') {
+                break;
+            }
+            branch.addClause(parseForm());
+        }
+
+        if (!peekable()) {
+            return new ParseError("unterminated branch", line);
+        }
+
+        advance();  // consume closing paren
+
+        return branch;
+    }
+
     Form parseAnd() {
         And and_ = new And(line);
         char next;
@@ -691,6 +727,8 @@ class Parser {
                     return parseBlock();
                 case "if":
                     return parseIf();
+                case "branch":
+                    return parseBranch();
                 case "and":
                     return parseAnd();
                 case "or":
-- 
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