evalexpr: initial recursive descent parser

src/ast/ast.c

@@ -0,0 +1,67 @@
+#include "ast.h"
+
+#include <stdlib.h>
+
+struct ast_node *make_num(int val)
+{
+    struct ast_node *ret = malloc(sizeof(*ret));
+
+    if (ret == NULL)
+        return ret;
+
+    ret->kind = NODE_NUM;
+    ret->val.num = val;
+
+    return ret;
+}
+
+struct ast_node *make_unop(enum unop_kind op, struct ast_node *tree)
+{
+    struct ast_node *ret = malloc(sizeof(*ret));
+
+    if (ret == NULL)
+        return ret;
+
+    ret->kind = NODE_UNOP;
+    ret->val.un_op.op = op;
+    ret->val.un_op.tree = tree;
+
+    return ret;
+}
+
+struct ast_node *make_binop(enum binop_kind op, struct ast_node *lhs,
+                            struct ast_node *rhs)
+{
+    struct ast_node *ret = malloc(sizeof(*ret));
+
+    if (ret == NULL)
+        return ret;
+
+    ret->kind = NODE_BINOP;
+    ret->val.bin_op.op = op;
+    ret->val.bin_op.lhs = lhs;
+    ret->val.bin_op.rhs = rhs;
+
+    return ret;
+}
+
+void destroy_ast(struct ast_node *ast)
+{
+    if (!ast)
+        return;
+
+    switch (ast->kind)
+    {
+    case NODE_BINOP:
+        destroy_ast(ast->val.bin_op.lhs);
+        destroy_ast(ast->val.bin_op.rhs);
+        break;
+    case NODE_UNOP:
+        destroy_ast(ast->val.un_op.tree);
+        /* fallthrough */
+    case NODE_NUM:
+        break;
+    }
+
+    free(ast);
+}

src/ast/ast.h

@@ -0,0 +1,61 @@
+#ifndef AST_H
+#define AST_H
+
+// Forward declaration
+struct ast_node;
+
+enum unop_kind
+{
+    UNOP_IDENTITY,
+    UNOP_NEGATE,
+    UNOP_FACT,
+};
+
+enum binop_kind
+{
+    BINOP_PLUS,
+    BINOP_MINUS,
+    BINOP_TIMES,
+    BINOP_DIVIDES,
+    BINOP_POW,
+};
+
+struct unop_node
+{
+    enum unop_kind op;
+    struct ast_node *tree;
+};
+
+struct binop_node
+{
+    enum binop_kind op;
+    struct ast_node *lhs;
+    struct ast_node *rhs;
+};
+
+struct ast_node
+{
+    enum node_kind
+    {
+        NODE_UNOP,
+        NODE_BINOP,
+        NODE_NUM,
+    } kind;
+    union ast_val
+    {
+        struct unop_node un_op;
+        struct binop_node bin_op;
+        int num;
+    } val;
+};
+
+struct ast_node *make_num(int val);
+
+struct ast_node *make_unop(enum unop_kind op, struct ast_node *tree);
+
+struct ast_node *make_binop(enum binop_kind op, struct ast_node *lhs,
+                            struct ast_node *rhs);
+
+void destroy_ast(struct ast_node *ast);
+
+#endif /* !AST_H */