From 9323c1285a8a9f7ec33e88d26f102d92c7a6e2ec Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Sun, 10 Oct 2021 14:15:45 +0200
Subject: Add cond special form

---
 examples/booleans.bdl       | 21 +++++++++++++++++++++
 src/bootstrap/main.c        |  2 ++
 src/bootstrap/primitives.c  | 26 +++++++++++++++++++++++++-
 tests/booleans_expected.txt |  5 +++++
 4 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/examples/booleans.bdl b/examples/booleans.bdl
index d526f25..24d57a0 100644
--- a/examples/booleans.bdl
+++ b/examples/booleans.bdl
@@ -54,3 +54,24 @@
 (print "(if (or (+ 1 2 3) false) (+ 1 2 3) (+ 7 8 9)) -> ") (if (or (+ 1 2 3) false) (+ 1 2 3) (+ 7 8 9))
 (print "(if true 7) -> ")                                   (if true 7)
 (print "(if false 7) -> ")                                  (if false 7)
+
+;; Cond.
+(print "(cond ((and true true true) 1) ((or true true false) 2) (else 3)) -> ")
+(cond ((and true true true) 1)
+      ((or true true false) 2)
+      (else 3))
+(print "(cond ((and true true false) 1) ((or true true false) 2) (else 3)) -> ")
+(cond ((and true true false) 1)
+      ((or true true false) 2)
+      (else 3))
+(print "(cond ((and true true false) 1) ((or false false false) 2) (else 3)) -> ")
+(cond ((and true true false) 1)
+      ((or false false false) 2)
+      (else 3))
+(print "(cond ((and true true true) 1) ((or true true false) 2)) -> ")
+(cond ((and true true false) 1)
+      ((or false false false) 2))
+(print "(cond ((and true true true) (+ 1 2 3)) ((or true true false) 2) (else 3)) -> ")
+(cond ((and true true true) (+ 1 2 3))
+      ((or true true false) 2)
+      (else 3))
diff --git a/src/bootstrap/main.c b/src/bootstrap/main.c
index 8ec1231..c0f2e50 100755
--- a/src/bootstrap/main.c
+++ b/src/bootstrap/main.c
@@ -41,6 +41,8 @@ init(void) {
     environment[env_n++] = (EnvSymbol){MAKE_SYM("and"), make_procedure(proc_and)};
     environment[env_n++] = (EnvSymbol){MAKE_SYM("or"), make_procedure(proc_or)};
     environment[env_n++] = (EnvSymbol){MAKE_SYM("if"), make_procedure(proc_if)};
+    environment[env_n++] = (EnvSymbol){MAKE_SYM("else"), obj_true};
+    environment[env_n++] = (EnvSymbol){MAKE_SYM("cond"), make_procedure(proc_cond)};
     environment[env_n++] = (EnvSymbol){MAKE_SYM("display"), make_procedure(proc_display)};
     environment[env_n++] = (EnvSymbol){MAKE_SYM("print"), make_procedure(proc_print)};
 }
diff --git a/src/bootstrap/primitives.c b/src/bootstrap/primitives.c
index 61ce360..29a1df8 100644
--- a/src/bootstrap/primitives.c
+++ b/src/bootstrap/primitives.c
@@ -329,6 +329,30 @@ proc_if(Object *args) {
     return obj_nil;
 }
 
-// TODO: cond
+Object *
+proc_cond(Object *args) {
+    if (args->type != OBJ_TYPE_PAIR) {
+        fprintf(stderr, "error: wrong number of arguments.\n");
+        return NULL;
+    }
+
+    if (args->car->type != OBJ_TYPE_PAIR) {
+        fprintf(stderr, "error: wrong argument type.\n");
+        return NULL;
+    }
+
+    while (args != obj_nil) {
+        Object *clause = args->car;
+        if (eval(clause->car) == obj_true) {
+            return eval(clause->cdr->car);
+        }
+
+        args = args->cdr;
+        clause = args->car;
+    }
+
+    return obj_nil;
+}
+
 // TODO: equality greater than smaller than...
 // TODO: fixnum left/right shift, mask, invert
diff --git a/tests/booleans_expected.txt b/tests/booleans_expected.txt
index d05d314..f0612b8 100644
--- a/tests/booleans_expected.txt
+++ b/tests/booleans_expected.txt
@@ -41,3 +41,8 @@
 (if (or (+ 1 2 3) false) (+ 1 2 3) (+ 7 8 9)) -> 6
 (if true 7) -> 7
 (if false 7) -> ()
+(cond ((and true true true) 1) ((or true true false) 2) (else 3)) -> 1
+(cond ((and true true false) 1) ((or true true false) 2) (else 3)) -> 2
+(cond ((and true true false) 1) ((or false false false) 2) (else 3)) -> 3
+(cond ((and true true true) 1) ((or true true false) 2)) -> ()
+(cond ((and true true true) (+ 1 2 3)) ((or true true false) 2) (else 3)) -> 6
-- 
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