From 32c489c957fc27d47bdb21eef6d7c971fe7fd0a3 Mon Sep 17 00:00:00 2001
From: Lephenixnoir <sebastien.michelland@protonmail.com>
Date: Sun, 8 Jan 2023 16:44:05 +0100
Subject: [PATCH] basic LL(1) parser for ASCII STL converter

---
 converters.py | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 converters.py

diff --git a/converters.py b/converters.py
new file mode 100644
index 0000000..d2e760e
--- /dev/null
+++ b/converters.py
@@ -0,0 +1,95 @@
+
+with open("humanoid.stl", "r") as fp:
+    stl = fp.read()
+
+#---
+
+class Lexer:
+    def __init__(self, data):
+        assert(data.startswith("solid"))
+        self.data = data
+        self.pos = min(80, data.index("\n"))
+
+    def lex(self):
+        # Skip leading whitespace
+        while self.pos < len(self.data) and self.data[self.pos] in " \t\n":
+            self.pos += 1
+
+        if self.pos >= len(self.data):
+            return None
+
+        # Grab a word
+        i = self.pos
+        while i < len(self.data) and self.data[i] not in " \t\n":
+            i += 1
+        word = self.data[self.pos:i]
+
+        self.pos = i
+        return float(word) if word[0] in "+-0123456789." else word
+
+#---
+
+class Parser:
+    def __init__(self, lexer):
+        self.lexer = lexer
+        self.la = "" # look-ahead token
+        self.feed()
+
+    def at_end(self):
+        return self.la == None
+
+    def feed(self):
+        t = self.la
+        self.la = lexer.lex()
+        return t
+
+    def expect_keyword(self, keyword):
+        assert self.la == keyword
+        self.feed()
+
+    def expect_float(self):
+        assert isinstance(self.la, float)
+        return self.feed()
+
+    #---
+
+    def vec3(self, leading_keyword):
+        self.expect_keyword(leading_keyword)
+        x = self.expect_float()
+        y = self.expect_float()
+        z = self.expect_float()
+        return (x, y, z)
+
+    def outer_loop(self):
+        self.expect_keyword("outer")
+        self.expect_keyword("loop")
+        v1 = self.vec3("vertex")
+        v2 = self.vec3("vertex")
+        v3 = self.vec3("vertex")
+        self.expect_keyword("endloop")
+        return [v1, v2, v3]
+
+    def facet(self):
+        self.expect_keyword("facet")
+        normal = self.vec3("normal")
+        vertices = self.outer_loop()
+        self.expect_keyword("endfacet")
+        return {"normal": normal, "vertices": vertices}
+
+    def solid(self):
+        facets = []
+        while self.la == "facet":
+            facets.append(self.facet())
+        self.expect_keyword("endsolid")
+        self.feed()
+        assert self.at_end()
+        return facets
+
+#---
+
+lexer = Lexer(stl)
+parser = Parser(lexer)
+
+solid = parser.solid()
+from pprint import pprint
+pprint(solid, width=90)