add binary lambda calculus parsing

igorw · igorw · commit baf681aa94f1 · 2013-12-22T22:12:05.000+01:00
diff --git a/composer.json b/composer.json
@@ -13,6 +13,6 @@
         "jakubledl/dissect": "dev-develop"
     },
     "autoload": {
-        "files": ["src/eval.php", "src/parser.php", "src/krivine.php"]
+        "files": ["src/eval.php", "src/parser.php", "src/krivine.php", "src/binary.php"]
     }
 }
diff --git a/composer.lock b/composer.lock
diff --git a/src/binary.php b/src/binary.php
@@ -0,0 +1,72 @@
+<?php
+
+namespace igorw\lambda\binary;
+
+// parse, return pair of [parsed, offset]
+// parsed uses de-bruijn indices
+function parse_term($bits)
+{
+    if ('00' === substr($bits, 0, 2)) {
+        list($body, $rest) = parse_term(substr($bits, 2));
+
+        return [
+            ['λ', $body],
+            $rest,
+        ];
+    }
+
+    if ('01' === substr($bits, 0, 2)) {
+        $rest = substr($bits, 2);
+        list($l, $rest) = parse_term($rest);
+        list($r, $rest) = parse_term($rest);
+
+        return [
+            [$l, $r],
+            $rest,
+        ];
+    }
+
+    if ('1' === $bits[0]) {
+        $i = 0;
+        while ($bits[++$i] !== '0');
+
+        return [
+            ['offset', $i],
+            substr($bits, $i + 1),
+        ];
+    }
+
+    throw new \InvalidArgumentException("Invalid binary term '$bits'");
+}
+
+function parse($bits)
+{
+    $bits = preg_replace('/\s/s', '', $bits);
+    list($parsed, $rest) = parse_term($bits);
+
+    if (strlen($rest) > 0) {
+        throw new \InvalidArgumentException("Non-closed binary term '$bits' had remaining part '$rest'");
+    }
+
+    return $parsed;
+}
+
+// identity
+// ['λ', ['offset', 1]]
+// var_dump(parse('0010'));
+
+// false
+// ['λ', ['λ', ['offset', 1]]]
+// var_dump(parse('000010'));
+
+// true
+// ['λ', ['λ', ['offset', 2]]]
+// var_dump(parse('0000110'));
+
+// λx.x x
+// ['λ', [['offset', 1], ['offset', 1]]]
+// var_dump(parse('00 01 10 10'));
+
+// λx.false
+// ['λ', ['λ', ['λ', ['offset', 1]]]]
+// var_dump(parse('00000010'));

Original file line number	Diff line number	Diff line change
`@@ -13,6 +13,6 @@`
`13`	`13`	`"jakubledl/dissect": "dev-develop"`
`14`	`14`	`},`
`15`	`15`	`"autoload": {`
`16`		`- "files": ["src/eval.php", "src/parser.php", "src/krivine.php"]`
	`16`	`+ "files": ["src/eval.php", "src/parser.php", "src/krivine.php", "src/binary.php"]`
`17`	`17`	`}`
`18`	`18`	`}`