From 2ac7ce05206b7e79b4be90de0d2f0988f4a155fd Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sat, 30 Nov 2019 18:06:07 +0100
Subject: [PATCH] calculator: add infix parser

---
 calculator/calculator/parse/__init__.py   |  1 +
 calculator/calculator/parse/infix.py      | 80 +++++++++++++++++++++++
 calculator/calculator/parse/test_infix.py | 42 ++++++++++++
 3 files changed, 123 insertions(+)
 create mode 100644 calculator/calculator/parse/infix.py
 create mode 100644 calculator/calculator/parse/test_infix.py

diff --git a/calculator/calculator/parse/__init__.py b/calculator/calculator/parse/__init__.py
index 630a813..c28704b 100644
--- a/calculator/calculator/parse/__init__.py
+++ b/calculator/calculator/parse/__init__.py
@@ -1,2 +1,3 @@
+from .infix import parse_infix
 from .postfix import parse_postfix
 from .prefix import parse_prefix
diff --git a/calculator/calculator/parse/infix.py b/calculator/calculator/parse/infix.py
new file mode 100644
index 0000000..0057f3f
--- /dev/null
+++ b/calculator/calculator/parse/infix.py
@@ -0,0 +1,80 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, List, Union, cast
+
+from calculator.ast import BinOp, Constant, UnaryOp
+from calculator.core import operations
+
+from .parsed_string import ParsedString
+
+if TYPE_CHECKING:
+    from calculator.ast import Node
+
+
+"""
+E : T [ (+|-) T ]*
+
+T : F [ (*|/) F ]*
+
+F : [ (-|+) ]* P
+
+P : G [ (^) F ]*
+
+G : '(' E ')' | CONSTANT
+"""
+
+
+def parse_g(l: List[Union[int, str]]) -> Node:
+    top = l.pop(0)
+    if top == "(":
+        ans = parse_e(l)
+        assert l.pop(0) == ")"
+        return ans
+    return Constant(top)
+
+
+def parse_p(l: List[Union[int, str]]) -> Node:
+    lhs = parse_g(l)
+    while len(l) and l[0] == "^":
+        op = l.pop(0)
+        rhs = parse_f(l)
+        lhs = BinOp(operations.STR_TO_BIN[op], lhs, rhs)
+    return lhs
+
+
+def parse_f(l: List[Union[int, str]]) -> Node:
+    str_to_unop = {
+        "+": operations.identity,
+        "-": operations.negate,
+    }
+    if l[0] in str_to_unop:
+        op = l.pop(0)
+        return UnaryOp(str_to_unop[op], parse_f(l))
+    return parse_p(l)
+
+
+def parse_t(l: List[Union[int, str]]) -> Node:
+    lhs = parse_f(l)
+    while len(l) and l[0] in ["*", "/"]:
+        op = cast(str, l.pop(0))
+        rhs = parse_t(l)
+        lhs = BinOp(operations.STR_TO_BIN[op], lhs, rhs)
+    return lhs
+
+
+def parse_e(l: List[Union[int, str]]) -> Node:
+    lhs = parse_t(l)
+    while len(l) and l[0] in ["+", "-"]:
+        op = cast(str, l.pop(0))
+        rhs = parse_t(l)
+        lhs = BinOp(operations.STR_TO_BIN[op], lhs, rhs)
+    return lhs
+
+
+def parse_infix(input: str) -> Node:
+    """
+    Parses the given string in infix notation.
+    """
+    parsed = ParsedString(input).tokenize()
+    ans = parse_e(parsed)
+    return ans
diff --git a/calculator/calculator/parse/test_infix.py b/calculator/calculator/parse/test_infix.py
new file mode 100644
index 0000000..1a3aed4
--- /dev/null
+++ b/calculator/calculator/parse/test_infix.py
@@ -0,0 +1,42 @@
+from calculator.ast import BinOp, Constant, UnaryOp
+from calculator.core import operations
+
+from .infix import parse_infix
+
+
+def test_parse_constant():
+    assert parse_infix("42") == Constant(42)
+
+
+def test_parse_negated_constant():
+    assert parse_infix("-42") == UnaryOp(operations.negate, Constant(42))
+
+
+def test_parse_doubly_negated_constant():
+    assert parse_infix("--42") == UnaryOp(
+        operations.negate, UnaryOp(operations.negate, Constant(42))
+    )
+
+
+def test_parse_binary_operation():
+    assert parse_infix("12 + 27") == BinOp(operations.plus, Constant(12), Constant(27))
+
+
+def test_parse_complete_expression_tree():
+    assert parse_infix("(12 + 27 )* (42 - 51)") == BinOp(
+        operations.times,
+        BinOp(operations.plus, Constant(12), Constant(27)),
+        BinOp(operations.minus, Constant(42), Constant(51)),
+    )
+
+
+def test_power_binds_to_the_right():
+    assert parse_infix("12 ^ 27 ^ 42") == BinOp(
+        operations.pow, Constant(12), BinOp(operations.pow, Constant(27), Constant(42))
+    )
+
+
+def test_negate_and_pow_dont_mix():
+    assert parse_infix("-12 ^ 27") == UnaryOp(
+        operations.negate, BinOp(operations.pow, Constant(12), Constant(27))
+    )