add concat and examples

examples/evalexpr.py

@@ -0,0 +1,89 @@
+#!/bin/env -S python
+
+from dataclasses import dataclass
+from typing import TypeVar, Union
+from os.path import dirname
+import sys
+
+sys.path.append(f"{dirname(__file__)}/../src")
+from pyalibert import regex, Parser, just, Declare
+
+# ast modeling
+
+@dataclass
+class OpAdd:
+    def apply(self, left: float, right: float): return left + right
+
+@dataclass
+class OpSub:
+    def apply(self, left: float, right: float): return left - right
+
+@dataclass
+class OpMul:
+    def apply(self, left: float, right: float): return left * right
+
+@dataclass
+class OpDiv:
+    def apply(self, left: float, right: float): return left / right
+
+@dataclass
+class BinOp:
+    actual: Union[OpAdd, OpSub, OpMul, OpDiv]
+    def apply(self, left: float, right: float): return self.actual.apply(left, right)
+
+@dataclass
+class Value:
+    actual: float
+
+@dataclass
+class Math:
+    first: "Expr"
+    rest: list[tuple[BinOp, "Expr"]]
+    def eval(self) -> float:
+        value = self.first.eval()
+        for (op, oth) in self.rest: value = op.apply(value, oth.eval())
+        return value
+
+@dataclass
+class Expr:
+    actual: Union[Value, Math]
+    def eval(self) -> float:
+        if isinstance(self.actual, Value): return self.actual.actual
+        else: return self.actual.eval()
+
+
+T = TypeVar("T")
+def lexeme(p: Parser[T]): return p << just(" ").repeat()
+
+none = just('')
+oper = lexeme(just("+").set(OpAdd()) | just("-").set(OpSub()) | just("*").set(OpMul()) | just("/").set(OpDiv())).map(BinOp)
+(lbrace, rbrace) = (lexeme(just('(')), lexeme(just(')')))
+
+digit = regex("[0-9]")
+integer = digit + digit.repeat().join()
+signed = (just("-") | none) + integer
+decimal = just(".") + integer
+value = lexeme(signed + (decimal | none)).map(float).map(Value)
+
+math = Declare[Math]()
+expr = (value | math.parser()).map(Expr)
+math_inner = (expr & (oper & expr).repeat()).map(lambda r: Math(*r))
+math.define(lbrace >> math_inner << rbrace)
+
+parser = math_inner
+
+
+def repl():
+    print("[   New super EvalExpr.   ]")
+    print("[ 100% composed and typed ]")
+    print("> ", end="")
+    sys.stdout.flush()
+    for line in sys.stdin:
+        result = parser.parse(line.strip())
+        print(result)
+        print(f"= {result.eval()}")
+        print("> ", end="")
+        sys.stdout.flush()
+
+
+if __name__ == "__main__": repl()