From 4c2be0ee13ce16c0274741f77c0d07ea768a2f64 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Thu, 23 Dec 2021 13:40:23 +0100
Subject: Add `if` compilation for ir

---
 src/ir.h | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/src/ir.h b/src/ir.h
index 514a3ac..c87babe 100644
--- a/src/ir.h
+++ b/src/ir.h
@@ -10,6 +10,7 @@ typedef enum Op {
     // Arithmetic ops.
     // - Binary operations.
     // - Arguments are passed via the stack.
+    // - Consume two items in the stack.
     OP_ADD,
     OP_SUB,
     OP_MUL,
@@ -18,7 +19,7 @@ typedef enum Op {
     // Logic ops.
     OP_NOT,
     // Stack ops.
-    // - Requires an Object to push into the stack.
+    // - Requires a constant Object to push into the stack.
     OP_PUSH,
     // - Discards the last value in the stack.
     OP_DROP,
@@ -34,8 +35,9 @@ typedef enum Op {
     OP_LABEL,
     // Jump/conditional ops.
     // - Take a label as argument.
-    // - For conditional jumps, the last value in the stack is used.
     OP_JUMP,
+    // - Consume one value in the stack.
+    // - All objects except `false` are considered `true`.
     OP_JUMP_IF_TRUE,
     OP_JUMP_IF_FALSE,
     // - These require numerical objects on the stack.
@@ -96,7 +98,7 @@ typedef struct Instruction {
 
         // OP_LABEL
         // OP_JUMP
-        // OP_JUMP_IF_FALSE
+        // OP_JUMP_IF_xxx
         size_t label_id;
     };
 
@@ -316,6 +318,7 @@ compile_proc_call(ProgramIr *program, Procedure *proc, Object *obj) {
             case BUILTIN_LE: {
                 compile_numeric_cmp(program, proc, OP_JUMP_IF_GT, line, col, obj->tail);
             } break;
+            // TODO: cons, car, cdr, type checks (nil? zero? fixnum? bool? ...)
             default: {
                 assert(false && "builtin not implemented");
             } break;
@@ -325,6 +328,23 @@ compile_proc_call(ProgramIr *program, Procedure *proc, Object *obj) {
     }
 }
 
+void
+compile_if(ProgramIr *program, Procedure *proc, Object *obj) {
+    size_t label_false = program->labels++;
+    compile_object(program, proc, obj->condition);
+    INST_ARG(proc, OP_JUMP_IF_FALSE, label_false, obj->line, obj->col);
+    compile_object(program, proc, obj->expr_true);
+    if (obj->expr_false != NULL) {
+        size_t label_exit = program->labels++;
+        INST_ARG(proc, OP_JUMP, label_exit, obj->line, obj->col);
+        INST_ARG(proc, OP_LABEL, label_false, obj->line, obj->col);
+        compile_object(program, proc, obj->expr_false);
+        INST_ARG(proc, OP_LABEL, label_exit, obj->line, obj->col);
+    } else {
+        INST_ARG(proc, OP_LABEL, label_false, obj->line, obj->col);
+    }
+}
+
 void
 compile_object(ProgramIr *program, Procedure *proc, Object *obj) {
     switch (obj->type) {
@@ -336,7 +356,7 @@ compile_object(ProgramIr *program, Procedure *proc, Object *obj) {
             INST_ARG(proc, OP_PUSH, obj, obj->line, obj->col);
         } break;
         case OBJ_TYPE_PAIR: { compile_proc_call(program, proc, obj); } break;
-        // case OBJ_TYPE_IF: { compile_if(obj); } break;
+        case OBJ_TYPE_IF: { compile_if(program, proc, obj); } break;
         // case OBJ_TYPE_LAMBDA: { compile_lambda(obj); } break;
         // case OBJ_TYPE_DEF: { compile_def(obj); } break;
         // case OBJ_TYPE_SYMBOL: { compile_symbol(obj); } break;
-- 
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