I'm trying to build something using macros ... my long goal is a
simple embedded DSL. Here's a simplified version:
(defmacro to-fn
"Converts a collection of forms into an anonymous function of no arguments."
[forms]
`(fn [] ~...@forms))
(defn run-example
[fn]
(printf "BEFORE\n")
(fn)
(printf "AFTER\n"))
(defmacro example
[& code]
`(let [fn# (to-fn ~code)]
(run-example fn#)))
(example (printf "EXAMPLE1\n") (printf "EXAMPLE2\n"))
This gives the expected output:
BEFORE
EXAMPLE1
EXAMPLE2
AFTER
Now, the problem is, I want to manipulate the list of forms passed to
the example macro before turning it into (to-fn) (the real DSL will
split the forms into groups and create multiple functions, and this is
all about the side-effects).
Changing the macro as so:
(defmacro example
[& code]
`(let [rcode# ~(reverse code)
fn# (to-fn rcode#)]
(run-example fn#)))
Give me an exception:
java.lang.RuntimeException: java.lang.RuntimeException:
java.lang.IllegalArgumentException: Don't know how to create ISeq
from: Symbol (p0-01.clj:42)
at clojure.lang.Compiler.analyze(Compiler.java:4032)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:4176)
at clojure.lang.Compiler.analyze(Compiler.java:4017)
at clojure.lang.Compiler.access$100(Compiler.java:38)
at clojure.lang.Compiler$LetExpr$Parser.parse(Compiler.java:3790)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:4188)
at clojure.lang.Compiler.analyze(Compiler.java:4017)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:4176)
at clojure.lang.Compiler.analyze(Compiler.java:4017)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:4176)
at clojure.lang.Compiler.analyze(Compiler.java:4017)
at clojure.lang.Compiler.analyze(Compiler.java:3978)
at clojure.lang.Compiler$BodyExpr$Parser.parse(Compiler.java:3678)
at clojure.lang.Compiler$FnMethod.parse(Compiler.java:3513)
at clojure.lang.Compiler$FnMethod.access$1100(Compiler.java:3390)
at clojure.lang.Compiler$FnExpr.parse(Compiler.java:2952)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:4186)
at clojure.lang.Compiler.analyze(Compiler.java:4017)
at clojure.lang.Compiler.eval(Compiler.java:4222)
at clojure.lang.Compiler.load(Compiler.java:4548)
at clojure.lang.Compiler.loadFile(Compiler.java:4515)
at clojure.main$load_script__5665.invoke(main.clj:206)
at clojure.main$script_opt__5696.invoke(main.clj:258)
at clojure.main$main__5720$fn__5722.invoke(main.clj:333)
at clojure.main$main__5720.doInvoke(main.clj:328)
at clojure.lang.RestFn.invoke(RestFn.java:413)
at clojure.lang.Var.invoke(Var.java:340)
at clojure.lang.AFn.applyToHelper(AFn.java:173)
at clojure.lang.Var.applyTo(Var.java:457)
at clojure.main.main(main.java:39)
Caused by: java.lang.RuntimeException: java.lang.RuntimeException:
java.lang.IllegalArgumentException: Don't know how to create ISeq
from: Symbol
at clojure.lang.LazySeq.seq(LazySeq.java:40)
at clojure.lang.Cons.next(Cons.java:37)
at clojure.lang.RT.count(RT.java:522)
at clojure.lang.Cons.count(Cons.java:47)
at clojure.lang.Compiler.analyze(Compiler.java:4008)
... 29 more
Caused by: java.lang.RuntimeException:
java.lang.IllegalArgumentException: Don't know how to create ISeq
from: Symbol
at clojure.lang.LazySeq.seq(LazySeq.java:40)
at clojure.lang.RT.seqFrom(RT.java:481)
at clojure.lang.RT.seq(RT.java:451)
at clojure.lang.LazySeq.seq(LazySeq.java:36)
... 33 more
Caused by: java.lang.IllegalArgumentException: Don't know how to
create ISeq from: Symbol
at clojure.lang.RT.seqFrom(RT.java:494)
at clojure.lang.RT.seq(RT.java:451)
at clojure.core$seq__3046.invoke(core.clj:107)
at clojure.core$concat__3174$cat__3188$fn__3189.invoke(core.clj:443)
at clojure.lang.LazySeq.seq(LazySeq.java:36)
... 36 more
I've thrashed on a number of variations, none of which do much better.
I feel I'm missing something subtle here. What is the right approach?
--
Howard M. Lewis Ship
Creator Apache Tapestry and Apache HiveMind
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