add abstract syntax tree code and some tests for it.

astree.c

@@ -0,0 +1,55 @@
+#include "astree.h"
+#include <stdlib.h>
+#include <stdio.h>
+
+struct astree *ast_create(int type, struct hm_item *symbol,
+	struct astree *c0,
+	struct astree *c1,
+	struct astree *c2,
+	struct astree *c3)
+{
+	struct astree *node = calloc(1, sizeof(struct astree));
+
+	if (!node) {
+		perror("astree: node alocation");
+		return NULL;
+	}
+
+	node->type = type;
+	node->symbol = symbol;
+	node->children[0] = c0;
+	node->children[1] = c1;
+	node->children[2] = c2;
+	node->children[3] = c3;
+
+	return node;
+}
+
+static const char *type_to_string[] = {
+	"symbol",
+	"+",
+	"-",
+	"*",
+	"/"
+};
+
+void ast_fprint(FILE *stream, int level, struct astree *tree) {
+	if (!tree) {
+		return;
+	}
+
+	int i;
+	for (i = 0; i < level; i++) {
+		fprintf(stream, "| ");
+	}
+
+	fprintf(stream, "%s", type_to_string[tree->type]);
+	if (tree->type == AST_SYM) {
+		fprintf(stream, ": %s", tree->symbol->key);
+	}
+	fprintf(stream, "\n");
+
+	for (i = 0; i < AST_MAXCHILDREN; i++) {
+		ast_fprint(stream, level + 1, tree->children[i]);
+	}
+}

astree.h

@@ -0,0 +1,31 @@
+#ifndef AST_H
+#define AST_H
+
+#include "hashmap.h"
+
+#define AST_MAXCHILDREN 4
+
+#define AST_SYM 0
+#define AST_ADD 1
+#define AST_SUB 2
+#define AST_MUL 3
+#define AST_DIV 4
+
+struct astree {
+	int type;
+	struct hm_item *symbol;
+	struct astree *children[AST_MAXCHILDREN];
+};
+
+/* Create a tree node with a type, a pointer to the symbol table
+ * and children.*/
+struct astree *ast_create(int type, struct hm_item *symbol,
+	struct astree *c0,
+	struct astree *c1,
+	struct astree *c2,
+	struct astree *c3);
+
+/* Pretty print a tree to a stream. */
+void ast_fprint(FILE *stream, int level, struct astree *tree);
+
+#endif /* ifndef AST_H */

hashmap.c

@@ -184,6 +184,12 @@ int hm_put(struct hashmap *hm, const char *key, const void *value) {
 	return -2;
 }
 
+struct hm_item *hm_getref(struct hashmap *hm, const char *key) {
+	struct hm_item **item = hm_find(hm, key);
+
+	return *item;
+}
+
 int hm_get(struct hashmap *hm, const char *key, void *value) {
 	struct hm_item **item = hm_find(hm, key);
 

hashmap.h

@@ -28,6 +28,9 @@ void hm_terminate(struct hashmap *hm);
 /* Insert (key, value) pair. */
 int hm_put(struct hashmap *hm, const char *key, const void *value);
 
+/* Retrieve a reference to an item */
+struct hm_item *hm_getref(struct hashmap *hm, const char *key);
+
 /* Retrive (key, value) pair. */
 int hm_get(struct hashmap *hm, const char *key, void *value);
 

tests/Makefile

@@ -1,11 +1,13 @@
-ALL_TARGETS := test_hashmap
+ALL_TARGETS := test_hashmap test_astree
 
 .PHONY = all
 all: $(ALL_TARGETS)
 
 test_hashmap: test_hashmap.c ../hashmap.c
 	gcc -I .. -o test_hashmap $^
-	./test_hashmap
+
+test_astree: test_astree.c ../hashmap.c ../astree.c
+	gcc -Wall -g -I .. -o test_astree $^
 
 .PHONY = clean
 clean:

tests/test_astree.c

@@ -0,0 +1,28 @@
+#include <stdlib.h>
+#include "astree.h"
+#include "hashmap.h"
+
+int main(int argc, char *argv[])
+{
+	struct hashmap map;
+	hm_initialize(10, 0.8, 1, &map);
+
+	/* put some garbage in the hashmap */
+	int n1, n2;
+	hm_put(&map, "1", &n1);
+	hm_put(&map, "2", &n2);
+	struct hm_item *s1 = hm_getref(&map, "1");
+	struct hm_item *s2 = hm_getref(&map, "2");
+
+	/* build 1 + 2 */
+	struct astree *t1 = ast_create(AST_SYM, s1, NULL, NULL, NULL, NULL);
+	struct astree *t2 = ast_create(AST_SYM, s2, NULL, NULL, NULL, NULL);
+	struct astree *sum = ast_create(AST_ADD, NULL, t1, t2, NULL, NULL);
+	ast_fprint(stderr, 0, sum);
+
+	hm_terminate(&map);
+	free(t1);
+	free(t2);
+	free(sum);
+	return 0;
+}