Extend .builtin syntax to allow for constructed values

This creates an ability to define variables with values that use
code to build a value rather than simply allowing a floating point
number. The value is specified with '= <poly_expr>', where
'<poly_expr>' is any C expression which returns a snek_poly_t value.

Signed-off-by: Keith Packard <keithp@keithp.com>

posix/snek-main.c

@@ -99,6 +99,8 @@ main (int argc, char **argv)
 		printf("Welcome to Snek version %s\n", SNEK_VERSION);
 	}
 
+	snek_init();
+
 	bool ret = snek_parse() == snek_parse_success;
 
 	if (snek_posix_input == stdin)

samd21/ao-snek.c

@@ -151,6 +151,7 @@ main(void)
 
 	setjmp(snek_reset_buf);
 	ao_snek_port_init();
+	snek_init();
 	snek_builtin_eeprom_load();
 	printf("Welcome to snek " SNEK_VERSION "\n");
 	fflush(stdout);

snek-builtin.py

@@ -27,7 +27,12 @@ class SnekBuiltin:
 
     def __init__(self, name, param, value):
         self.name = name
-        self.value = value
+        self.value = None
+        self.init = None
+        if value and value[0] == '=':
+            self.init = value[1:]
+        else:
+            self.value = value
         self.id = -1
         if param[0].isalpha():
             self.keyword = param
@@ -45,6 +50,9 @@ def is_name(self):
     def is_value(self):
         return self.nformal == -2 and self.value is not None
 
+    def is_init(self):
+        return self.nformal == -2 and self.init is not None
+
     def is_func(self):
         return self.nformal >= -1
 
@@ -111,13 +119,28 @@ def load_builtins(filename):
             bits = line.split(",")
             value = None
             if len(bits) > 2:
-                value = bits[2].strip()
+                value = ",".join(bits[2:]).strip()
             add_builtin(bits[0].strip(), bits[1].strip(), value)
 
 def dump_headers(fp):
     for line in headers:
         fprint("%s" % line, file=fp)
 
+def dump_init(fp):
+    use_list_build = False
+    fprint("#define snek_init() {\\", file=fp)
+    for name in sorted(builtins):
+        if name.is_init():
+            if 'snek_list_build' in name.init:
+                use_list_build = True
+            fprint("    {\\", file=fp)
+            fprint("        snek_stack_push((%s));\\" % name.init, file=fp)
+            fprint("        *snek_id_ref(%s, true) = snek_stack_pop();\\" % name.cpp_name(), file=fp)
+            fprint("    }\\", file=fp)
+    fprint("}", file=fp)
+    if use_list_build:
+        fprint("#define SNEK_LIST_BUILD", file=fp)
+
 def dump_max_len(fp):
     max_len = 0
     for name in builtins:
@@ -258,6 +281,8 @@ def builtin_main():
 
     dump_headers(fp)
 
+    dump_init(fp)
+
     fprint("#ifndef SNEK_BUILTIN_NFORMAL", file=fp)
     fprint("#define SNEK_BUILTIN_NFORMAL(b) ((b)->nformal)", file=fp)
     fprint("#define SNEK_BUILTIN_FUNCV(b) ((b)->funcv)", file=fp)

snek-duino/snek-duino.c

@@ -113,6 +113,7 @@ main (void)
 	stderr = stdout = stdin = &snek_duino_file;
 	snek_uart_init();
 	port_init();
+	snek_init();
 	for (;;)
 		snek_parse();
 }

windows/snek-windows.c

@@ -95,6 +95,8 @@ main (int argc, char **argv)
 		printf("Welcome to Snek version %s\n", SNEK_VERSION);
 	}
 
+	snek_init();
+
 	bool ret = snek_parse() == snek_parse_success;
 
 	if (snek_windows_input == stdin)