diff --git a/crates/generate/.gitignore b/crates/generate/.gitignore
new file mode 100644
index 0000000000..eb5a316cbd
--- /dev/null
+++ b/crates/generate/.gitignore
@@ -0,0 +1 @@
+target
diff --git a/crates/generate/Cargo.toml b/crates/generate/Cargo.toml
index 2403f089a8..cd720d549c 100644
--- a/crates/generate/Cargo.toml
+++ b/crates/generate/Cargo.toml
@@ -12,3 +12,4 @@ witx = { path = "../WASI/tools/witx" }
 quote = "1.0"
 proc-macro2 = "1.0"
 heck = "0.3"
+anyhow = "1"
diff --git a/crates/generate/src/imp.rs b/crates/generate/src/imp.rs
index 24f9ee6c2f..bd980c139b 100644
--- a/crates/generate/src/imp.rs
+++ b/crates/generate/src/imp.rs
@@ -3,8 +3,6 @@ use proc_macro2::{Delimiter, Group, Literal, TokenStream, TokenTree};
 use quote::{format_ident, quote};
 use std::convert::TryFrom;
 
-const WITX_PATH: &'static str = "crates/WASI/phases/snapshot/witx/wasi_snapshot_preview1.witx";
-
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum Mode {
     Host,
@@ -21,15 +19,8 @@ impl Mode {
     }
 }
 
-pub fn gen() -> TokenStream {
+pub fn gen(doc: witx::Document) -> TokenStream {
     let mut output = TokenStream::new();
-    let doc = match witx::load(&[&WITX_PATH]) {
-        Ok(doc) => doc,
-        Err(e) => {
-            panic!("error opening file {}: {}", WITX_PATH, e);
-        }
-    };
-
     gen_datatypes(&mut output, &doc, Mode::Wasi);
     // gen_datatypes(&mut output, &doc, Mode::Wasi32);
     // gen_datatypes(&mut output, &doc, Mode::Host);
diff --git a/crates/generate/src/lib.rs b/crates/generate/src/lib.rs
index 8e214f3345..f3b9a93f5f 100644
--- a/crates/generate/src/lib.rs
+++ b/crates/generate/src/lib.rs
@@ -1,10 +1,16 @@
 extern crate proc_macro;
 
 mod imp;
+mod parse;
 
 use proc_macro::TokenStream;
+use proc_macro2::TokenStream as TokenStream2;
 
 #[proc_macro]
-pub fn from_witx(_args: TokenStream) -> TokenStream {
-    TokenStream::from(imp::gen())
+pub fn from_witx(args: TokenStream) -> TokenStream {
+    let args = TokenStream2::from(args);
+    let witx_paths = parse::witx_paths(args).expect("parsing macro arguments");
+    let doc = witx::load(&witx_paths).expect("loading witx");
+    let out = imp::gen(doc);
+    TokenStream::from(out)
 }
diff --git a/crates/generate/src/parse.rs b/crates/generate/src/parse.rs
new file mode 100644
index 0000000000..65c8a190cc
--- /dev/null
+++ b/crates/generate/src/parse.rs
@@ -0,0 +1,33 @@
+use anyhow::{bail, Result};
+use proc_macro2::{Literal, TokenStream, TokenTree};
+
+pub fn witx_paths(args: TokenStream) -> Result<Vec<String>> {
+    let arg_strings = args
+        .into_iter()
+        .map(|arg| match arg {
+            TokenTree::Literal(lit) => string_literal(lit),
+            _ => bail!("expected string literal, got: {:?}", arg),
+        })
+        .collect::<Result<Vec<String>>>()?;
+
+    if arg_strings.is_empty() {
+        bail!("expected at least one argument");
+    }
+    Ok(arg_strings)
+}
+
+fn string_literal(literal: Literal) -> Result<String> {
+    let s = literal.to_string();
+    if !s.starts_with('"') || !s.ends_with('"') {
+        bail!("string literal must be enclosed in double quotes");
+    }
+
+    let trimmed = s[1..s.len() - 1].to_owned();
+    if trimmed.contains('"') {
+        bail!("string literal must not contain quotes");
+    }
+    if trimmed.contains('\\') {
+        bail!("string literal must not contain backslashes");
+    }
+    Ok(trimmed)
+}
diff --git a/src/lib.rs b/src/lib.rs
index 0136867e5c..4c58828ac7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,2 +1,8 @@
-generate::from_witx!();
-
+pub mod test {
+    generate::from_witx!("test.witx");
+}
+/*
+pub mod wasi {
+    generate::from_witx!("crates/WASI/phases/snapshot/witx/wasi_snapshot_preview1.witx");
+}
+*/
diff --git a/test.witx b/test.witx
new file mode 100644
index 0000000000..f1185b63fe
--- /dev/null
+++ b/test.witx
@@ -0,0 +1,13 @@
+
+
+(typename $errno
+    (enum u32
+        $dont_want_to
+        $physically_unable
+        $picket_line))
+
+(module $foo
+  (@interface func (export "bar")
+    (param $name string)
+    (result $error $errno))
+)