diff --git a/src/bin/ponderosa-asm.rs b/src/bin/ponderosa-asm.rs
index 9459417..7c0047c 100644
--- a/src/bin/ponderosa-asm.rs
+++ b/src/bin/ponderosa-asm.rs
@@ -7,6 +7,20 @@ use std::collections::{HashMap, BTreeMap, VecDeque};
 
 use ponderosa::state::{Land, Rule};
 
+macro_rules! ad_hoc_rule {
+    ($tokens:expr, $argument_count:expr, $body:block) => {
+        if $tokens.len() < $argument_count {
+            Err("Too few arguments".to_owned())
+        } else if $tokens.len() > $argument_count {
+            Err("Too many arguments".to_owned())
+        } else {
+            #[allow(unused)]
+            let parse_rule = |tokens: &Vec<&str>| -> Result<u16, String> {$body};
+            parse_rule($tokens)
+        }
+    };
+}
+
 macro_rules! assert_argument_count {
     ($tokens:expr, $count:expr) => {
         if $tokens.len() < $count {
@@ -17,20 +31,17 @@ macro_rules! assert_argument_count {
             return Err("Too many arguments".to_owned());
         }
     };
-    
-    ($tokens:expr, $count:expr, $body:block) => {
-        if $tokens.len() < $count {
-            Err("Too few arguments".to_owned());
-        } else if $tokens.len() > $count {
-            Err("Too many arguments".to_owned());
-        } else $body
-    };
 }
 
 fn parse_number(string: &str) -> u16 {
     string.parse::<u16>().unwrap()
 }
 
+fn parse_safely<T: std::str::FromStr>(string: &str) -> Result<T, String> {
+    string.parse::<T>()
+        .map_err(|_| format!("Cannot parse number: {t}", t=string))
+}
+
 fn stack_bit(token: &str) -> Result<u16, String> {
     let c = token.as_bytes()[0] as char;
     match c {
@@ -54,11 +65,8 @@ fn parse_binary_op(tokens: &Vec<&str>, opcode: u16, signed: bool) -> Result<u16,
 fn parse_binary_immediate_op(tokens: &Vec<&str>, opcode: u16, signed: bool) -> Result<u16, String> {
     assert_argument_count!(tokens, 4);
 
-    let signed_immediate = tokens[2].parse::<i16>()
-        .map_err(|_| format!("Cannot parse number: {t}", t=tokens[2]))?;
-
-    let unsigned_immediate = tokens[2].parse::<u16>()
-        .map_err(|_| format!("Cannot parse number: {t}", t=tokens[2]))?;
+    let signed_immediate = parse_safely::<i16>(tokens[2])?;
+    let unsigned_immediate = parse_safely::<u16>(tokens[2])?;
 
     if signed {
         if signed_immediate < -32 || signed_immediate > 31 {
@@ -82,11 +90,8 @@ fn parse_push(tokens: &Vec<&str>, opcode: u16, signed: bool) -> Result<u16, Stri
     assert_argument_count!(tokens, 3);
 
     let dest = stack_bit(tokens[1])?;
-    let signed_immediate = tokens[2].parse::<i16>()
-        .map_err(|_| format!("Cannot parse number: {t}", t=tokens[2]))?;
-
-    let unsigned_immediate = tokens[2].parse::<u16>()
-        .map_err(|_| format!("Cannot parse number: {t}", t=tokens[2]))?;
+    let signed_immediate = parse_safely::<i16>(tokens[2])?;
+    let unsigned_immediate = parse_safely::<u16>(tokens[2])?;
 
     let immediate = if signed { signed_immediate as u16 } else { unsigned_immediate };
 
@@ -111,11 +116,8 @@ fn parse_forestry_op(tokens: &Vec<&str>, opcode: u16) -> Result<u16, String> {
     assert_argument_count!(tokens, 4);
 
     let stack = stack_bit(tokens[1])?;
-    let relative_x = tokens[2].parse::<i16>()
-        .map_err(|_| format!("Cannot parse number: {t}", t=tokens[2]))?;
-
-    let relative_y = tokens[3].parse::<i16>()
-        .map_err(|_| format!("Cannot parse number: {t}", t=tokens[2]))?;
+    let relative_x = parse_safely::<i16>(tokens[2])?;
+    let relative_y = parse_safely::<i16>(tokens[3])?;
 
     if relative_x > 15 || relative_x < -16 {
         Err(format!("Cannot reach cell at {relative_x} along the X-axis; trees may only access cells in the range of -16 to 15"))
@@ -210,7 +212,7 @@ fn main() -> io::Result<()> {
                 "mult" => parse_binary_op(&tokens, 0b00111, true),
                 "div"  => parse_binary_op(&tokens, 0b01000, true),
                 "slt"  => parse_binary_op(&tokens, 0b01001, true),
-                "not"  => assert_argument_count!(tokens, 3, {
+                "not"  => ad_hoc_rule!(&tokens, 3, {
                     let opcode = 0b10010;
                     let (src, dest) = (stack_bit(tokens[1])?, stack_bit(tokens[2])?);
                     Ok(opcode<<11 & src<<9 & dest<<8)
@@ -244,23 +246,20 @@ fn main() -> io::Result<()> {
                 "swap"   => parse_stack_op(&tokens, 0b01111),
                 "rotate" => parse_stack_op(&tokens, 0b10000),
                 "flip"   => parse_stack_op(&tokens, 0b10001),
-                "clear"  => {
+                "clear"  => ad_hoc_rule!(&tokens, 2, {
                     let opcode = 0b10010;
-                    assert_argument_count!(tokens, 2);
                     let to_clear = stack_bit(tokens[1])?;
                     Ok(opcode<<11 | to_clear<<10)
-                },
+                }),
 
-                "skip" => {
+                "skip" => ad_hoc_rule!(&tokens, 2, {
                     let opcode = 0b10011;
-                    assert_argument_count!(tokens, 2);
-                    Ok(opcode<<11 | (tokens[1].parse::<u16>() & 0b111111111))
-                },
-                "skim" => {
+                    Ok(opcode<<11 | (parse_safely::<u16>(tokens[1])? & 0b111111111))
+                }),
+                "skim" => ad_hoc_rule!(&tokens, 2, {
                     let opcode = 0b10100;
-                    assert_argument_count!(tokens, 2);
                     Ok(opcode<<11 | stack_bit(tokens[1])? << 9)
-                },
+                }),
 
                 "sow"       => parse_forestry_op(&tokens, 0b10101),
                 "reap"      => parse_forestry_op(&tokens, 0b10110),
@@ -268,11 +267,10 @@ fn main() -> io::Result<()> {
                 "replant"   => parse_forestry_op(&tokens, 0b11000),
                 "yield"     => Ok(0b11001_0_00000_00000),
                 "compost"   => Ok(0b11010_0_00000_00000),
-                "define" => {
+                "define" => ad_hoc_rule!(&tokens, 2, {
                     let opcode = 0b11011;
-                    assert_argument_count!(tokens, 2);
                     Ok(opcode<<11 | stack_bit(tokens[1])? << 10)
-                },
+                }),
 
                 "wait"     => parse_forestry_op(&tokens, 0b11100),
                 "signal"   => parse_forestry_op(&tokens, 0b11101),