commit 704979f9bbc8252f26796b1befdd0f86f2e1858e
Author: tovjemam <gitea@deadfish.cz>
Date:   Sun Oct 13 19:32:55 2024 +0200

    init

diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..43a2f8e
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,29 @@
+# Minimum required CMake version
+cmake_minimum_required(VERSION 3.10)
+
+# Project name and version
+project(Graph VERSION 1.0)
+
+# Specify the C standard
+set(CMAKE_C_STANDARD 90)
+set(CMAKE_C_STANDARD_REQUIRED True)
+
+# Add the executable target
+add_executable(Graph
+    "main.c"
+    "lex.c"
+    "parser.c"
+    "tree.c"
+)
+
+# Optionally, you can set compiler warnings
+if (MSVC)
+    target_compile_options(Graph PRIVATE /W4)
+else()
+    target_compile_options(Graph PRIVATE -Wall -Wextra -pedantic)
+endif()
+
+# Optionally, set the output directory for the executable
+# set_target_properties(Graph PROPERTIES
+#     RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin"
+# )
\ No newline at end of file
diff --git a/lex.c b/lex.c
new file mode 100644
index 0000000..37067d5
--- /dev/null
+++ b/lex.c
@@ -0,0 +1,191 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "lex.h"
+
+struct lexer {
+    const char* start;
+    const char* prev_p;
+    const char* p;
+    struct token tok;
+};
+
+struct lexer *lex_create(const char *str) {
+    struct lexer *lex = malloc(sizeof(struct lexer));
+
+    if (!lex)
+        return NULL;
+
+    lex->start = str;
+    lex->prev_p = str;
+    lex->p = str;
+    
+    lex_next(lex);
+
+    return lex;
+}
+
+void lex_free(struct lexer *lex) {
+    free(lex);
+}
+
+static int is_whitespace(char p) {
+    return p == ' ' || p == '\t' || p == '\n' || p == '\r';
+}
+
+static void skip_whitespace(struct lexer *lex) {
+    while (is_whitespace(*lex->p))
+        ++lex->p;
+}
+
+static int try_advance(struct lexer *lex, const char *str) {
+    const char *temp_p = lex->p;
+    while (1) {
+        if (!*str) {
+            lex->p = temp_p;
+            return 1;
+        }
+
+        if (*str != *temp_p) {
+            return 0;
+        }
+
+        ++temp_p;
+        ++str;
+    }
+}
+
+static int try_token(struct lexer *lex, const char *tok_str, enum token_type type) {
+    if (try_advance(lex, tok_str)) {
+        lex->tok.type = type;
+        return 1;
+    }
+    return 0;
+}
+
+static int try_fn(struct lexer *lex, const char *tok_str, enum math_fn fn) {
+    if (try_advance(lex, tok_str)) {
+        lex->tok.type = TOK_FUNCTION;
+        lex->tok.val.fn = fn;
+        return 1;
+    }
+    return 0;
+}
+
+static int try_number(struct lexer* lex) {
+    char *end;
+    double val;
+    val = strtod(lex->p, &end);
+    if (lex->p == end) return 0;
+    lex->tok.type = TOK_NUMBER;
+    lex->tok.val.num = val;
+    lex->p = end;
+    return 1;
+}
+
+void lex_next(struct lexer *lex) {
+    skip_whitespace(lex);
+    lex->prev_p = lex->p;
+
+    if (!*lex->p) {
+        lex->tok.type = TOK_EOF;
+        return;
+    }
+
+    if (try_token(lex, "+", TOK_PLUS)) return;
+    if (try_token(lex, "-", TOK_MINUS)) return;
+    if (try_token(lex, "*", TOK_MULTIPLY)) return;
+    if (try_token(lex, "/", TOK_DIVIDE)) return;
+    if (try_token(lex, "^", TOK_POWER)) return;
+    
+    if (try_token(lex, "x", TOK_X)) return;
+
+    if (try_token(lex, "(", TOK_LEFT_PAREN)) return;
+    if (try_token(lex, ")", TOK_RIGHT_PAREN)) return;
+
+    if (try_fn(lex, "abs", FN_ABS)) return;
+    if (try_fn(lex, "exp", FN_EXP)) return;
+    if (try_fn(lex, "ln", FN_LN)) return;
+    if (try_fn(lex, "log", FN_LOG)) return;
+    if (try_fn(lex, "sinh", FN_SINH)) return;
+    if (try_fn(lex, "sin", FN_SIN)) return;
+    if (try_fn(lex, "cosh", FN_COSH)) return;
+    if (try_fn(lex, "cos", FN_COS)) return;
+    if (try_fn(lex, "tanh", FN_TANH)) return;
+    if (try_fn(lex, "tan", FN_TAN)) return;
+    if (try_fn(lex, "asin", FN_ASIN)) return;
+    if (try_fn(lex, "acos", FN_ACOS)) return;
+    if (try_fn(lex, "atan", FN_ATAN)) return;
+
+    if (try_number(lex)) return;
+
+    fprintf(stderr, "Lexer error - unrecognized sequence \"%s\"\n", lex->p);
+    lex_print_position(lex);
+
+    lex->tok.type = TOK_ERROR;
+    return;
+}
+
+struct token *lex_token(struct lexer *lex) {
+    return &lex->tok;
+}
+
+void lex_print_position(struct lexer *lex) {
+    int i;
+    int pos = lex->prev_p - lex->start;
+    
+    fprintf(stderr, "At character %d\n", pos);
+    fprintf(stderr, "   %s\n", lex->start);
+    fprintf(stderr, "   ");
+    for (i = 0; i < pos; ++i)
+        fprintf(stderr, " ");
+
+    fprintf(stderr, "^\n----------------------------------------------------\n");
+}
+
+
+#ifdef LEX_DEBUG
+
+void lex_debug_print_token(struct token *tok) {
+    static const char *token_str[] = {
+        "TOK_EOF",
+        "TOK_ERROR",
+        "TOK_NUMBER",
+        "TOK_PLUS",
+        "TOK_MINUS",
+        "TOK_MULTIPLY",
+        "TOK_DIVIDE",
+        "TOK_POWER",
+        "TOK_X",
+        "TOK_FUNCTION",
+        "TOK_LEFT_PAREN",
+        "TOK_RIGHT_PAREN"
+    };
+
+    static const char *fn_str[] = {
+        "FN_ABS",
+        "FN_EXP",
+        "FN_LN",
+        "FN_LOG",
+        "FN_SIN",
+        "FN_COS",
+        "FN_TAN",
+        "FN_ASIN",
+        "FN_ACOS",
+        "FN_ATAN",
+        "FN_SINH",
+        "FN_COSH",
+        "FN_TANH"
+    };
+
+    printf("%-20s ", token_str[tok->type]);
+
+    if (tok->type == TOK_NUMBER)
+        printf("%.2f\n", tok->val.num);
+    else if (tok->type == TOK_FUNCTION)
+        printf("%s\n", fn_str[tok->val.fn]);
+    else
+        printf("\n");
+}
+
+#endif /* LEX_DEBUG */
\ No newline at end of file
diff --git a/lex.h b/lex.h
new file mode 100644
index 0000000..cc5dca6
--- /dev/null
+++ b/lex.h
@@ -0,0 +1,61 @@
+#ifndef LEX_H
+#define LEX_H
+
+#define LEX_DEBUG
+
+enum token_type {
+    TOK_EOF,
+    TOK_ERROR,
+
+    TOK_NUMBER,
+    TOK_PLUS,
+    TOK_MINUS,
+    TOK_MULTIPLY,
+    TOK_DIVIDE,
+    TOK_POWER,
+    TOK_X,
+    TOK_FUNCTION,
+    TOK_LEFT_PAREN,
+    TOK_RIGHT_PAREN
+};
+
+enum math_fn {
+    FN_ABS,
+    FN_EXP,
+    FN_LN,
+    FN_LOG,
+    FN_SIN,
+    FN_COS,
+    FN_TAN,
+    FN_ASIN,
+    FN_ACOS,
+    FN_ATAN,
+    FN_SINH,
+    FN_COSH,
+    FN_TANH
+};
+
+struct token {
+    enum token_type type;
+    union token_val {
+        double num;
+        enum math_fn fn;
+    } val;
+};
+
+struct lexer;
+
+extern struct lexer *lex_create(const char *str);
+extern void lex_free(struct lexer *lex);
+
+extern void lex_next(struct lexer *lex);
+extern struct token *lex_token(struct lexer *lex);
+
+extern void lex_print_position(struct lexer *lex);
+
+
+#ifdef LEX_DEBUG
+extern void lex_debug_print_token(struct token *tok);
+#endif /* LEX_DEBUG */
+
+#endif /* LEX_H */
\ No newline at end of file
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..1b46599
--- /dev/null
+++ b/main.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "lex.h"
+#include "parser.h"
+
+int main(int argc, char *argv[]) { 
+
+    struct lexer *lex;
+    struct expr_node *node;
+
+    if (argc < 2) {
+        printf("Usage: %s <expression>\n", argv[0]);
+        return 1;
+    }
+
+    /*
+    //struct lexer *lex = lex_create("x* sin  (x  ^ 2) * 5.5e+2* cosh (x )");
+    //struct lexer *lex = lex_create("-1 + -2 - 3 + 4");
+    */
+    lex = lex_create(argv[1]);
+
+    node = parse_expression(lex);
+    lex_free(lex);
+
+    if (node) {
+        double x;
+        node_debug_print(node);
+        printf("polygon(");
+        for (x = -10.0; x < 10.0; x += 0.1) {
+            printf("(%.2f,%.2f),", x, node_eval(node, x));
+        }
+        printf("(10, -1000),(-10,-1000))\n");
+    }
+
+    node_free(node);
+
+    return 0;
+}
\ No newline at end of file
diff --git a/parser.c b/parser.c
new file mode 100644
index 0000000..399b700
--- /dev/null
+++ b/parser.c
@@ -0,0 +1,263 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include "parser.h"
+
+static int token_is(struct lexer *lex, enum token_type type) {
+    return lex_token(lex)->type == type;
+}
+
+static int accept(struct lexer *lex, enum token_type type) {
+    if (token_is(lex, type)) {
+        lex_next(lex);
+        return 1;
+    }
+    return 0;
+}
+
+static double token_num(struct lexer *lex) {
+    return lex_token(lex)->val.num;
+}
+
+static enum math_fn token_fn(struct lexer *lex) {
+    return lex_token(lex)->val.fn;
+}
+
+static void error_expected_one_of(struct lexer *lex, const int expected[], enum token_type got) {
+    static const char* token_name[] = {
+        "end of expression",
+        "lexer error",
+        "constant",
+        "+",
+        "-",
+        "*",
+        "/",
+        "^",
+        "x",
+        "function name",
+        "(",
+        ")"
+    };
+
+    int separate = 0;
+
+    fprintf(stderr, "Syntax error - expected ");
+
+    for (; *expected >= 0; ++expected) {
+        if (separate)
+            fprintf(stderr, ", ");
+        else
+            separate = 1;
+
+        fprintf(stderr, "'%s'", token_name[*expected]);
+    }
+
+    fprintf(stderr, " - but got '%s'\n", token_name[got]);
+
+    lex_print_position(lex);
+}
+
+static void error_expected_single(struct lexer *lex, enum token_type expected, enum token_type got) {
+    static int expected_arr[] = { -1, -1 };
+    expected_arr[0] = expected;
+    error_expected_one_of(lex, expected_arr, got);
+}
+
+struct expr_node *parse_subexpression(struct lexer *lex);
+
+static struct expr_node *parse_bracketed(struct lexer* lex) {
+    struct expr_node *node;
+
+    if (!accept(lex, TOK_LEFT_PAREN)) {
+        error_expected_single(lex, TOK_LEFT_PAREN, lex_token(lex)->type);
+        return NULL;
+    }
+
+    if (!(node = parse_subexpression(lex)))
+        return NULL;
+
+    if (!accept(lex, TOK_RIGHT_PAREN)) {
+        error_expected_single(lex, TOK_RIGHT_PAREN, lex_token(lex)->type);
+        node_free(node);
+        return NULL;
+    }
+
+    return node;
+}
+
+static struct expr_node *parse_base(struct lexer *lex) {
+    struct expr_node *inner;
+    
+    if (token_is(lex, TOK_NUMBER)) {
+        double val = token_num(lex);
+        lex_next(lex);
+        return node_create_const(val);
+    }
+
+    if (accept(lex, TOK_X)) {
+        return node_create_x();
+    }
+
+    if (token_is(lex, TOK_FUNCTION)) {
+        enum math_fn fn = token_fn(lex);
+        lex_next(lex);
+
+        if (!(inner = parse_bracketed(lex)))
+            return NULL;
+
+        return node_create_fn(fn, inner);
+    }
+
+    if (token_is(lex, TOK_LEFT_PAREN)) {
+        return parse_bracketed(lex);
+    }
+
+    {
+        static const int expected[] = { TOK_NUMBER, TOK_X, TOK_FUNCTION, TOK_LEFT_PAREN, -1 };
+        error_expected_one_of(lex, expected, lex_token(lex)->type);
+    }
+
+    return NULL;
+}
+
+static struct expr_node* parse_unary(struct lexer *lex) {
+    if (accept(lex, TOK_MINUS)) {
+        struct expr_node *node, *inner;
+        
+        if (!(inner = parse_base(lex)))
+            return NULL;
+
+        if (!(node = node_create_neg(inner))) {
+            node_free(inner);
+            return NULL;
+        }
+
+        return node;
+    }
+
+    accept(lex, TOK_PLUS);
+    return parse_base(lex);
+}
+
+static struct expr_node *parse_factor(struct lexer *lex) {
+    struct expr_node *node, *new_node, *inner;
+
+    if (!(node = parse_unary(lex)))
+        return NULL;
+
+    while (accept(lex, TOK_POWER)) {
+        if (!(inner = parse_unary(lex))) {
+            node_free(node);
+            return NULL;
+        }
+
+        if (!(new_node = node_create_pow(node, inner))) {
+            node_free(node);
+            node_free(inner);
+            return NULL;
+        }
+
+        node = new_node;
+    }
+
+    return node;
+}
+
+static struct expr_node *parse_term(struct lexer *lex) {
+    struct expr_node *node, *new_node, *inner;
+
+    if (!(node = parse_factor(lex)))
+        return NULL;
+
+    while (1) {
+        struct expr_node *(*create_node)(struct expr_node *left, struct expr_node *right);
+
+        if (accept(lex, TOK_MULTIPLY))
+            create_node = node_create_mult;
+        else if (accept(lex, TOK_DIVIDE))
+            create_node = node_create_div;
+        else
+            break;
+
+        if (!(inner = parse_factor(lex))) {
+            node_free(node);
+            return NULL;
+        }
+
+        if (!(new_node = create_node(node, inner))) {
+            node_free(node);
+            node_free(inner);
+            return NULL;
+        }
+
+        node = new_node;
+    }
+
+    return node;
+}
+
+struct expr_node *parse_subexpression(struct lexer *lex) {
+    struct expr_node *node, *new_node, *inner;
+    
+    /*
+    if (accept(lex, TOK_MINUS)) {
+        if (!(term = parse_term(lex)))
+            return NULL;
+
+        if (!(node = node_create_neg(term))) {
+            node_free(term);
+            return NULL;
+        }
+    }
+    else {
+        accept(lex, TOK_PLUS);
+
+        if (!(node = parse_term(lex)))
+            return NULL;
+    }
+    
+    */
+
+    if (!(node = parse_term(lex)))
+        return NULL;
+
+    while (1) {
+        struct expr_node *(*create_node)(struct expr_node *left, struct expr_node *right);
+
+        if (accept(lex, TOK_PLUS))
+            create_node = node_create_add;
+        else if (accept(lex, TOK_MINUS))
+            create_node = node_create_sub;
+        else
+            break;
+
+        if (!(inner = parse_term(lex))) {
+            node_free(node);
+            return NULL;
+        }
+
+        if (!(new_node = create_node(node, inner))) {
+            node_free(node);
+            node_free(inner);
+            return NULL;
+        }
+
+        node = new_node;
+    }
+
+    return node;
+}
+
+struct expr_node *parse_expression(struct lexer *lex) {
+    struct expr_node *node;
+
+    if (!(node = parse_subexpression(lex)))
+        return NULL;
+
+    if (!token_is(lex, TOK_EOF)) {
+        error_expected_single(lex, TOK_EOF, lex_token(lex)->type);
+        node_free(node);
+        return NULL;
+    }
+
+    return node;
+}
\ No newline at end of file
diff --git a/parser.h b/parser.h
new file mode 100644
index 0000000..f070592
--- /dev/null
+++ b/parser.h
@@ -0,0 +1,8 @@
+#ifndef PARSER_H
+#define PARSER_H
+
+#include "tree.h"
+
+extern struct expr_node *parse_expression(struct lexer *lex);
+
+#endif /* PARSER_H */
\ No newline at end of file
diff --git a/tree.c b/tree.c
new file mode 100644
index 0000000..6989833
--- /dev/null
+++ b/tree.c
@@ -0,0 +1,232 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <math.h>
+#include "tree.h"
+
+static struct expr_node *alloc_node(void) {
+    return malloc(sizeof(struct expr_node));
+}
+
+struct expr_node *node_create_const(double val) {
+    struct expr_node *node = alloc_node();
+    if (!node) return NULL;
+    node->type = EXPR_CONST;
+    node->vals.num = val;
+    return node;
+}
+
+struct expr_node *node_create_neg(struct expr_node *unop) {
+    struct expr_node *node = alloc_node();
+    if (!node) return NULL;
+    node->type = EXPR_NEG;
+    node->vals.unop = unop;
+    return node;
+}
+
+static struct expr_node *create_binary_node(enum expr_type type, struct expr_node *left, struct expr_node *right) {
+    struct expr_node *node = alloc_node();
+    if (!node) return NULL;
+    node->type = type;
+    node->vals.binop.left = left;
+    node->vals.binop.right = right;
+    return node;
+}
+
+struct expr_node *node_create_add(struct expr_node *left, struct expr_node *right) {
+    return create_binary_node(EXPR_ADD, left, right);
+}
+
+struct expr_node *node_create_sub(struct expr_node *left, struct expr_node *right) {
+    return create_binary_node(EXPR_SUB, left, right);
+}
+
+struct expr_node *node_create_mult(struct expr_node *left, struct expr_node *right) {
+    return create_binary_node(EXPR_MULT, left, right);
+}
+
+struct expr_node *node_create_div(struct expr_node *left, struct expr_node *right) {
+    return create_binary_node(EXPR_DIV, left, right);
+}
+
+struct expr_node *node_create_pow(struct expr_node *base, struct expr_node *power) {
+    return create_binary_node(EXPR_POW, base, power);
+}
+
+struct expr_node *node_create_x(void) {
+    struct expr_node *node = alloc_node();
+    if (!node) return NULL;
+    node->type = EXPR_X;
+    return node;
+}
+
+struct expr_node *node_create_fn(enum math_fn fn, struct expr_node *arg) {
+    struct expr_node *node = alloc_node();
+    if (!node) return NULL;
+    node->type = EXPR_FN;
+    node->vals.fn.fn = fn;
+    node->vals.fn.arg = arg;
+    return node;
+}
+
+void node_free(struct expr_node *node) {
+    if (!node) return;
+
+    switch (node->type) {
+        case EXPR_ADD:
+        case EXPR_SUB:
+        case EXPR_MULT:
+        case EXPR_DIV:
+        case EXPR_POW:
+            node_free(node->vals.binop.left);
+            node_free(node->vals.binop.right);
+            break;
+
+        case EXPR_NEG:
+            node_free(node->vals.unop);
+            break;
+
+        case EXPR_FN:
+            node_free(node->vals.fn.arg);
+            break;
+
+        default:
+            break;
+    }
+
+    free(node);
+}
+
+static void debug_indent(int indent) {
+    int i;
+    for (i = 0; i < indent; ++i)
+        printf("   ");
+}
+
+static void debug_print(struct expr_node *node, int indent);
+
+static void debug_print_binop(struct expr_node *node, const char* name, int indent) {
+    debug_indent(indent); printf("[%s]\n", name);
+    /*debug_indent(indent); printf("left:\n");*/
+    debug_print(node->vals.binop.left, indent + 1);
+    /*debug_indent(indent); printf("right:\n");*/
+    debug_print(node->vals.binop.right, indent + 1);
+}
+
+static void debug_print(struct expr_node *node, int indent) {
+    static const char* fn_str[] = {
+        "FN_ABS",
+        "FN_EXP",
+        "FN_LN",
+        "FN_LOG",
+        "FN_SIN",
+        "FN_COS",
+        "FN_TAN",
+        "FN_ASIN",
+        "FN_ACOS",
+        "FN_ATAN",
+        "FN_SINH",
+        "FN_COSH",
+        "FN_TANH"
+    };
+
+    switch (node->type) {
+        case EXPR_ADD:
+            debug_print_binop(node, "ADD", indent);
+            break;
+
+        case EXPR_SUB:
+            debug_print_binop(node, "SUB", indent);
+            break;
+
+        case EXPR_MULT:
+            debug_print_binop(node, "MULT", indent);
+            break;
+
+        case EXPR_DIV:
+            debug_print_binop(node, "DIV", indent);
+            break;
+
+        case EXPR_POW:
+            debug_print_binop(node, "POW", indent);
+            break;
+
+        case EXPR_NEG:
+            debug_indent(indent); printf("[NEG]\n");
+            /*debug_indent(indent); printf("unop:\n");*/
+            debug_print(node->vals.unop, indent + 1);
+            break;
+
+        case EXPR_CONST:
+            debug_indent(indent); printf("[CONST] %.2f\n", node->vals.num);
+            break;
+
+        case EXPR_X:
+            debug_indent(indent); printf("[X]\n");
+
+            break;
+
+        case EXPR_FN:
+            debug_indent(indent); printf("[FN] %s\n", fn_str[node->vals.fn.fn]);
+            /*debug_indent(indent); printf("arg:\n");*/
+            debug_print(node->vals.fn.arg, indent + 1);
+            break;
+
+        default:
+            break;
+    }
+}
+
+
+void node_debug_print(struct expr_node *node) {
+    debug_print(node, 0);
+}
+
+double node_eval(struct expr_node *node, double x) {
+    switch (node->type) {
+        case EXPR_CONST:
+            return node->vals.num;
+
+        case EXPR_X:
+            return x;
+
+        case EXPR_NEG:
+            return -node_eval(node->vals.unop, x);
+
+        case EXPR_ADD:
+            return node_eval(node->vals.binop.left, x) + node_eval(node->vals.binop.right, x);
+
+        case EXPR_SUB:
+            return node_eval(node->vals.binop.left, x) - node_eval(node->vals.binop.right, x);
+
+        case EXPR_MULT:
+            return node_eval(node->vals.binop.left, x) * node_eval(node->vals.binop.right, x);
+
+        case EXPR_DIV:
+            return node_eval(node->vals.binop.left, x) / node_eval(node->vals.binop.right, x);
+
+        case EXPR_POW:
+            return pow(node_eval(node->vals.binop.left, x), node_eval(node->vals.binop.right, x));
+
+        case EXPR_FN:
+        {
+            double inner = node_eval(node->vals.fn.arg, x);
+            switch (node->vals.fn.fn) {
+                case FN_ABS: return fabs(inner);
+                case FN_EXP: return exp(inner);
+                case FN_LN: return log(inner);
+                case FN_LOG: return log10(inner);
+                case FN_SIN: return sin(inner);
+                case FN_COS: return cos(inner);
+                case FN_TAN: return tan(inner);
+                case FN_ASIN: return asin(inner);
+                case FN_ACOS: return acos(inner);
+                case FN_ATAN: return atan(inner);
+                case FN_SINH: return sinh(inner);
+                case FN_COSH: return cosh(inner);
+                case FN_TANH: return tanh(inner);
+            }
+        }
+    }
+
+    return 0.0;
+}
diff --git a/tree.h b/tree.h
new file mode 100644
index 0000000..cd9be8f
--- /dev/null
+++ b/tree.h
@@ -0,0 +1,51 @@
+#ifndef TREE_H
+#define TREE_H
+
+#include "lex.h"
+
+enum expr_type {
+    EXPR_CONST,
+    EXPR_NEG,
+    EXPR_ADD,
+    EXPR_SUB,
+    EXPR_MULT,
+    EXPR_DIV,
+    EXPR_POW,
+    EXPR_X,
+    EXPR_FN
+};
+
+struct expr_node {
+    enum expr_type type;
+    union expr_vals {
+        struct expr_binop_vals {
+            struct expr_node *left;
+            struct expr_node *right;
+        } binop;
+        struct expr_fn_vals {
+            enum math_fn fn;
+            struct expr_node *arg;
+        } fn;
+        struct expr_node *unop;
+        double num;
+    } vals;
+};
+
+extern struct expr_node *node_create_const(double val);
+extern struct expr_node *node_create_neg(struct expr_node *unop);
+extern struct expr_node *node_create_add(struct expr_node *left, struct expr_node *right);
+extern struct expr_node *node_create_sub(struct expr_node *left, struct expr_node *right);
+extern struct expr_node *node_create_mult(struct expr_node *left, struct expr_node *right);
+extern struct expr_node *node_create_div(struct expr_node *left, struct expr_node *right);
+extern struct expr_node *node_create_pow(struct expr_node *base, struct expr_node *power);
+extern struct expr_node *node_create_x(void);
+extern struct expr_node *node_create_fn(enum math_fn fn, struct expr_node *arg);
+
+extern void node_debug_print(struct expr_node *node);
+
+extern double node_eval(struct expr_node *node, double x);
+
+extern void node_free(struct expr_node *node);
+
+
+#endif /* TREE_H */
\ No newline at end of file