commit 83c75de773b94f9ac0ddfc90295432e36e08a401
Author: Bruno BELANYI <bruno@belanyi.fr>
Date:   Sun Nov 8 16:55:12 2020 +0100

    pratt: add parser
    
    This is based on C's operator precedence rules

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..2c4c7ad
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,22 @@
+CC = gcc
+CPPFLAGS = -Isrc/ -D_POSIX_C_SOURCE=200809L
+VPATH = src/
+CFLAGS = -Wall -Wextra -pedantic -Werror -std=c99
+USE_CLIMBING = 1
+
+SRC = \
+    src/eval.c \
+
+BIN = pratt
+OBJ = $(SRC:.c=.o)
+
+.PHONY: all
+all: $(BIN)
+
+$(BIN):
+$(BIN): $(OBJ) src/pratt.o
+
+.PHONY: clean
+clean:
+	$(RM) $(OBJ) # remove object files
+	$(RM) $(BIN) # remove main program
diff --git a/src/eval.c b/src/eval.c
new file mode 100644
index 0000000..e3439f7
--- /dev/null
+++ b/src/eval.c
@@ -0,0 +1,269 @@
+#include <ctype.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <string.h>
+
+#define UNREACHABLE() __builtin_unreachable()
+#define ARR_SIZE(Arr) (sizeof(Arr) / sizeof(*Arr))
+#define OP_STRING(...) (const char[]){__VA_ARGS__}
+#define OP_SIZE(...) (sizeof(OP_STRING(__VA_ARGS__)) - 1)
+
+typedef bool (nul_f)(const char **input, int *res, int until);
+typedef bool (left_f)(int lhs, const char **input, int *res, int until);
+
+// Define the different tokens
+enum token_kind {
+#define OP(Name, ...) Name,
+#include "operators.inc"
+};
+
+struct token {
+    enum token_kind kind;
+    int val; // Used for NUMBER
+};
+
+// Forward declare functions
+#define NulFunc(Name) \
+    static nul_f eval_ ## Name ## _nul;
+#define LeftFunc(Name) \
+    static left_f eval_ ## Name ## _left;
+
+#define PREFIX_POSTFIX(Name)  \
+    NulFunc(Name) \
+    LeftFunc(Name)
+#define PREFIX(Name)  \
+    NulFunc(Name)
+#define PREFIX_INFIX(Name)  \
+    NulFunc(Name) \
+    LeftFunc(Name)
+#define INFIX(Name)  \
+    LeftFunc(Name)
+#define TERN(Name)  \
+    LeftFunc(Name)
+#define PAREN(Name) \
+    NulFunc(Name)
+#define NOT_OP(Name)
+# define OP(Name, NulPrio, LeftPrio, Type, ...) \
+    Type(Name)
+#include "operators.inc"
+
+#undef NulFunc
+#undef LeftFunc
+
+// Symbol table
+static const struct {
+    const char *op;
+    const size_t op_len;
+    const int nul_prio;
+    const int left_prio;
+    nul_f *const nul_func;
+    left_f *const left_func;
+} ops[] = {
+#define NulFunc(Name) \
+    eval_ ## Name ## _nul
+#define LeftFunc(Name) \
+    eval_ ## Name ## _left
+
+#define PREFIX_POSTFIX(Name, NulPrio, LeftPrio, ...)  \
+    [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NulFunc(Name), LeftFunc(Name), },
+#define PREFIX(Name, NulPrio, LeftPrio, ...)  \
+    [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NulFunc(Name), NULL, },
+#define PREFIX_INFIX(Name, NulPrio, LeftPrio, ...)  \
+    [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NulFunc(Name), LeftFunc(Name), },
+#define INFIX(Name, NulPrio, LeftPrio, ...)  \
+    [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NULL, LeftFunc(Name), },
+#define TERN(Name, NulPrio, LeftPrio, ...)  \
+    [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NULL, LeftFunc(Name), },
+#define PAREN(Name, NulPrio, LeftPrio, ...) \
+    [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NulFunc(Name), NULL, },
+#define NOT_OP(Name, NulPrio, LeftPrio, ...) \
+    [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NULL, NULL, },
+# define OP(Name, NulPrio, LeftPrio, Type, Operator, /* Operator String */ ...) \
+    Type(Name, NulPrio, LeftPrio, __VA_ARGS__)
+#include "operators.inc"
+
+#undef LeftFunc
+#undef NulFunc
+};
+
+// Lexing functions
+static void skip_whitespace(const char **input) {
+    while (*input[0] && isspace(*input[0]))
+        *input += 1; // Skip this character
+}
+
+static bool expect(enum token_kind expected, const char **input) {
+    skip_whitespace(input);
+
+    if (strncmp(*input, ops[expected].op, ops[expected].op_len) != 0)
+        return false;
+
+    *input += ops[expected].op_len;
+    return true;
+}
+
+static size_t my_atoi(const char **input, int *val) {
+    size_t len = 0;
+
+    *val = 0; // Initialize its value
+    while (isdigit((*input)[len]))
+    {
+        *val *= 10;
+        *val += (*input)[len] - '0';
+        len += 1;
+    };
+
+    return len;
+}
+
+static size_t lex_operator(const char **input, enum token_kind *op) {
+    size_t best_len = 0;
+
+    for (size_t i = 0; i < ARR_SIZE(ops); ++i)
+    {
+        if (ops[i].op_len <= best_len) // Only look at longer operators
+            continue;
+        if (strncmp(*input, ops[i].op, ops[i].op_len) == 0)
+        {
+            best_len = ops[i].op_len;
+            *op = i;
+        }
+    }
+
+    return best_len;
+}
+
+static size_t lex_token(const char **input, struct token *tok) {
+    skip_whitespace(input);
+
+    size_t len;
+
+    if ((len = lex_operator(input, &tok->kind)))
+        return len;
+
+    // Assume that it is a number
+    tok->kind = NUMBER;
+    return my_atoi(input, &tok->val);
+}
+
+static bool parse_until_left(int lhs, const char **input, int *res, int prio) {
+    struct token tok;
+    size_t len = 0;
+
+    while ((len = lex_token(input, &tok)) &&
+            prio < ops[tok.kind].left_prio) {
+        *input += len;
+        left_f *left_func = ops[tok.kind].left_func;
+        if (!left_func)
+            return false; // Error: not a prefix operator
+        if (!left_func(lhs, input, res, prio))
+            return false; // Error: could not parse right-hand-side
+        lhs = *res;
+    }
+
+    return true;
+}
+static bool parse_until(const char **input, int *res, int prio) {
+    struct token tok;
+    size_t len = 0;
+
+    // Parse left token
+    if (!(len = lex_token(input, &tok)))
+        return false;
+
+    // Assume prefix
+    *input += len;
+    if (tok.kind == NUMBER) {
+        *res = tok.val;
+    } else {
+        nul_f *nul_func = ops[tok.kind].nul_func;
+        if (!nul_func)
+            return false; // Error: not a prefix operator
+        nul_func(input, res, prio);
+    }
+
+    // Do left-loop
+    return parse_until_left(*res, input, res, prio);
+}
+
+bool eval_string(const char *input, int *res) {
+    if (!parse_until(&input, res, 0))
+        return false;
+    // Verify that only the expression exists
+    skip_whitespace(&input);
+    return *input == '\0';
+}
+
+#define NulFunc(Name) \
+    static bool eval_ ## Name ## _nul( \
+            const char **input, \
+            int *res, \
+            __attribute__((unused)) int until)
+#define LeftFunc(Name) \
+    static bool eval_ ## Name ## _left( \
+            int lhs, \
+            const char **input, \
+            int *res, \
+            __attribute__((unused)) int until)
+
+#define PREFIX_POSTFIX(Name, NulPrio, LeftPrio, Operator)  \
+    LeftFunc(Name) { \
+        return parse_until_left(lhs Operator, input, res, LeftPrio); \
+    } \
+    NulFunc(Name) { \
+        if (!parse_until(input, res, NulPrio)) \
+            return false; \
+        Operator *res; \
+        return true; \
+    }
+#define PREFIX(Name, NulPrio, LeftPrio, Operator)  \
+    NulFunc(Name) { \
+        if (!parse_until(input, res, NulPrio)) \
+            return false; \
+        *res = Operator *res; \
+        return true; \
+    }
+#define PREFIX_INFIX(Name, NulPrio, LeftPrio, Operator)  \
+    LeftFunc(Name) { \
+        if (!parse_until(input, res, LeftPrio)) \
+            return false; \
+        *res = lhs Operator *res; \
+        return true; \
+    } \
+    NulFunc(Name) { \
+        if (!parse_until(input, res, NulPrio)) \
+            return false; \
+        *res = Operator *res; \
+        return true; \
+    }
+#define INFIX(Name, NulPrio, LeftPrio, Operator) \
+    LeftFunc(Name) { \
+        if (!parse_until(input, res, LeftPrio)) \
+            return false; \
+        *res = lhs Operator *res; \
+        return true; \
+    }
+#define TERN(Name, NulPrio, LeftPrio, Operator) \
+    LeftFunc(Name) { \
+        int true_val; \
+        if (!parse_until(input, &true_val, 0) || !expect(COLON, input)) \
+            return false; \
+        int false_val; \
+        if (!parse_until(input, &false_val, until)) \
+            return false; \
+        *res = (lhs ? true_val : false_val); \
+        return true; \
+    }
+#define PAREN(Name, NulPrio, LeftPrio, Operator) \
+    NulFunc(Name) { \
+        if (!parse_until(input, res, 0)) \
+            return false; \
+        return expect(R_PAREN, input); \
+    }
+#define NOT_OP(Name, NulPrio, LeftPrio, Operator) /* Nothing */
+# define OP(Name, NulPrio, LeftPrio, Type, Operator, ...) \
+    Type(Name, NulPrio, LeftPrio, Operator)
+#include "operators.inc"
+
+#undef LeftFunc
+#undef NulFunc
diff --git a/src/eval.h b/src/eval.h
new file mode 100644
index 0000000..cd0d57d
--- /dev/null
+++ b/src/eval.h
@@ -0,0 +1,8 @@
+#ifndef ONCE_H
+#define ONCE_H
+
+#include <stdbool.h>
+
+bool eval_string(const char *input, int *res);
+
+#endif /* !ONCE_H */
diff --git a/src/operators.inc b/src/operators.inc
new file mode 100644
index 0000000..08b217e
--- /dev/null
+++ b/src/operators.inc
@@ -0,0 +1,45 @@
+/*
+ * 10 '?:' ternary (set to 0 in middle)
+ *
+ * Do not use any assignation yet
+ */
+#ifndef OP
+# define OP(Name, NulPrio, LeftPrio, Type, Operator, /* Operator String */ ...)
+#endif
+
+// Simple operators
+OP(  PLUS_PLUS, 120, 110, PREFIX_POSTFIX,          ++, '+', '+', 0)
+OP(MINUS_MINUS, 120, 110, PREFIX_POSTFIX,          --, '-', '-', 0)
+OP(        NOT, 120,  -1,         PREFIX,           !, '!', 0)
+OP(    BIT_NOT, 120,  -1,         PREFIX,           ~, '~', 0)
+OP(       PLUS, 110,  90,   PREFIX_INFIX,           +, '+', 0)
+OP(      MINUS, 110,  90,   PREFIX_INFIX,           -, '-', 0)
+OP(       TIMES, -1, 100,          INFIX,           *, '*', 0)
+OP(     DIVIDES, -1, 100,          INFIX,           /, '/', 0)
+OP(      MODULO, -1, 100,          INFIX,           %, '%', 0)
+OP(  LEFT_SHIFT, -1,  80,          INFIX,          <<, '<', '<', 0)
+OP( RIGHT_SHIFT, -1,  80,          INFIX,          >>, '>', '>', 0)
+OP(       EQUAL, -1,  70,          INFIX,          ==, '=', '=', 0)
+OP(   NOT_EQUAL, -1,  70,          INFIX,          !=, '!', '=', 0)
+OP(     BIT_AND, -1,  60,          INFIX,           &, '&', 0)
+OP(     BIT_XOR, -1,  50,          INFIX,           ^, '^', 0)
+OP(      BIT_OR, -1,  40,          INFIX,           |, '|', 0)
+OP(         AND, -1,  30,          INFIX,          &&, '&', '&', 0)
+OP(          OR, -1,  20,          INFIX,          ||, '|', '|', 0)
+// Special operators
+OP(     TERNARY, -1,  10,           TERN, PLACEHOLDER, '?', 0)
+OP(       COLON, -1,  -1,         NOT_OP, PLACEHOLDER, ':', 0)
+OP(     L_PAREN,  0,   0,          PAREN, PLACEHOLDER, '(', 0)
+OP(     R_PAREN, -1,  -1,         NOT_OP, PLACEHOLDER, ')', 0)
+// Special tokens
+OP(      NUMBER,  0,  -1,         NOT_OP, PLACEHOLDER, 0)
+
+#undef OP
+
+#undef PREFIX_POSTFIX
+#undef PREFIX
+#undef PREFIX_INFIX
+#undef INFIX
+#undef TERN
+#undef PAREN
+#undef NOT_OP
diff --git a/src/pratt.c b/src/pratt.c
new file mode 100644
index 0000000..837592a
--- /dev/null
+++ b/src/pratt.c
@@ -0,0 +1,28 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "eval.h"
+
+int main(void)
+{
+    char *line = NULL;
+    size_t size = 0;
+    ssize_t ret = 0;
+
+    while ((getline(&line, &size, stdin)) > 0)
+    {
+        int res;
+        if (!eval_string(line, &res))
+        {
+            fputs("Could not parse input\n", stderr);
+            ret = 1;
+            continue;
+        }
+
+        printf("%d\n", res);
+    }
+
+    free(line);
+
+    return ret;
+}