4 files changed, 38 insertions(+), 14 deletions(-)

M include/eval.h
M src/env.c
M src/eval.c
M src/parser.c

@@ 2,7 2,11 @@
 #define SUSHI_EVAL_H
 
 struct expression;
-struct binding;
+struct binding {
+	char *name;
+	struct expression *expr;
+	struct binding *next;
+};
 
 /*
  * Evaluates an expression.


@@ 13,7 17,7 @@ struct binding;
  */
 struct expression *eval(struct expression *expr, struct binding **);
 
-struct expression *binding_lookup(struct binding *binds, char *symbol);
+struct binding *binding_lookup(struct binding *binds, char *symbol);
 void binding_insert(struct binding **binds, char *symbol,
 	struct expression *value);
 

@@ 284,6 284,30 @@ env_define(struct location loc, struct list_expression *list,
 }
 
 static struct expression *
+env_set(struct location loc, struct list_expression *list,
+	struct binding **bindings)
+{
+	if (!list || !list->next) {
+		error(loc, "Not enough arguments");
+	}
+
+	struct expression *handle = list->expr;
+	if (handle->kind != EXPR_SYMBOL) {
+		error(loc, "Invalid set!; expected a symbol");
+	}
+	struct expression *value = eval(list->next->expr, bindings);
+
+	struct binding *bind = binding_lookup(*bindings, handle->symbol);
+	if (!bind) {
+		error(loc, "Undefined symbol '%s'", handle->symbol);
+	}
+	expression_free(bind->expr);
+	bind->expr = value;
+
+	return mknil();
+}
+
+static struct expression *
 env_if(struct location loc, struct list_expression *list,
 	struct binding **bindings)
 {


@@ 393,6 417,7 @@ environment[] = {
 	{ .name = "or",  .func = &env_or },
 
 	{ .name = "define", .func = &env_define },
+	{ .name = "set!",   .func = &env_set },
 	{ .name = "if",     .func = &env_if },
 
 	{ .name = "cons", .func = &env_cons },

@@ 2,22 2,17 @@
 #include <stdbool.h>
 #include <string.h>
 #include "env.h"
+#include "eval.h"
 #include "expr.h"
 #include "parser.h"
 #include "utils.h"
 
-struct binding {
-	char *name;
-	struct expression *expr;
-	struct binding *next;
-};
-
-struct expression *
+struct binding *
 binding_lookup(struct binding *binds, char *symbol)
 {
 	while (binds) {
 		if (strcmp(binds->name, symbol) == 0) {
-			return binds->expr;
+			return binds;
 		}
 
 		binds = binds->next;


@@ 100,12 95,11 @@ eval(struct expression *expr, struct binding **bindings)
 	case EXPR_LIST:
 		return eval_list(expr, bindings);
 	case EXPR_SYMBOL: {
-		struct expression *value = binding_lookup(*bindings,
-			expr->symbol);
-		if (!value) {
+		struct binding *bind = binding_lookup(*bindings, expr->symbol);
+		if (!bind) {
 			return mknil();
 		}
-		return expression_dup(value);
+		return expression_dup(bind->expr);
 	}
 	case EXPR_QUOTE:
 		return expression_dup(expr->quoted);

@@ 149,6 149,7 @@ is_symbol(char ch, bool start)
 		|| ch == '<'
 		|| ch == '_'
 		|| ch == '-'
+		|| ch == '!'
 		|| (start ? false : isdigit(ch));
 }