From 7560aac5007f30f11717893821b0455fbb8003b0 Mon Sep 17 00:00:00 2001
From: Jeremy Penner <jeremy@sporktania.com>
Date: Mon, 4 Dec 2023 20:40:52 -0500
Subject: [PATCH] Undefined function defs and if statements

---
 README.md | 33 +++++++++++++++++++++++++++------
 go.fnl    | 31 ++++++++++++-------------------
 terra.fnl | 28 +++++++++++++++++++++++-----
 3 files changed, 62 insertions(+), 30 deletions(-)

diff --git a/README.md b/README.md
index 4c9b6cd..07d5825 100644
--- a/README.md
+++ b/README.md
@@ -18,15 +18,15 @@ I could maybe be persuaded to make `def` work like `fn` and optionally define a
 eh, whatever.
 
 ### def
-Defines a function, compiling down to the `terra` keyword.
+Defines a function, compiling down to the `terra` keyword. Can also be used to create an undefined 
+function, if called with no statements.
 
-Syntax:
 ```fennel
+; syntax:
 (def [argname1 argtype1 argname2 argtype2... : rettype1 rettype2...] statement...)
-```
+(def [argtype1 argtype2... : rettype1 rettype2...])
 
-Simple example:
-```fennel
+; examples:
 (local add (def [x int y int : int]
     (return (+ x y))))
 
@@ -36,10 +36,31 @@ Simple example:
 ; end
 
 (add 1 2) ; returns 3
+
+(local iseven (def [uint32 : bool]))
+(local isodd (def [n uint32 : bool]
+    (if (= n 0) 
+        (return true)
+        (return (iseven (- n 1))))))
+(iseven:adddefinition (def [n uint32 : bool]
+    (if (= n 0)
+        (return false)
+        (return (isodd (- n 1))))))
+
+; compiles to: 
+; local terra iseven :: { uint32 } -> { bool }
+; local isodd = terra(n : uint32) : { bool }
+;   if n == 0 then return true else return iseven(n - 1) end
+; end
+; iseven:adddefinition(terra(n : uint32) : { bool }
+;   if n == 0 then return false else return isodd(n - 1) end
+; end)
 ```
 
 To define a function as returning "void", simply end the argument list with a `:`.
-To make terra infer the return type, do not include a `:` in the argument list at all.
+To make terra infer the return type, do not include a `:` in the argument list at all. 
+Undefined functions can't have their return types inferred.
+
 Unlike Fennel, we do not implement implicit return semantics, and early returns are A-OK.
 Sorry Phil.
 
diff --git a/go.fnl b/go.fnl
index 944e053..43dc9f0 100644
--- a/go.fnl
+++ b/go.fnl
@@ -1,22 +1,15 @@
 (local fennel (require :fennel))
 (import-macros {: def : q : ttype : static : unterra : untype} :terra)
 
-(local Complex (ttype {real float imag float})) 
-(print (unterra
-  (def [: Complex] (return (Complex { real 5 imag 1 })))
-))
-(print (unterra
-  (def [c Complex r float] (tset c :real r))
-))
-(local thing (def [: Complex] (return (Complex { real 5 imag 1 }))))
-(local get-real (def [val Complex] (return (. val :real))))
-(local set-real (def [c [Complex] r float] (tset c :real r)))
-
-(let [result (thing)]
-  (print result result.real result.imag (get-real result))
-  (set-real result 10)
-  (print (get-real result)))
-
-(print (unterra 
-  (def [: int bool] (return 5 true))
-))
+(local iseven (def [uint32 : bool]))
+(local isodd (def [n uint32 : bool]
+    (if (= n 0) 
+        (return true)
+        (return (iseven (- n 1))))))
+(iseven:adddefinition (def [n uint32 : bool]
+    (if (= n 0)
+        (return false)
+        (return (isodd (- n 1))))))
+(print iseven)
+(print (iseven 5) (isodd 5))
+(print (iseven 6) (isodd 6))
diff --git a/terra.fnl b/terra.fnl
index 51c123f..ce20130 100644
--- a/terra.fnl
+++ b/terra.fnl
@@ -184,11 +184,13 @@
     (scope:with #(block :do stmts :end scope #(comp.expr $1 scope))))
 
 (fn forms.def [[arglist & stmts] scope]
-    (scope:with #(let [(in out) (split-arglist arglist)
-                       argpairs (fcollect [i 1 (length in) 2] {:name (. in i) :type (. in (+ i 1))})
-                       rettyp  (if out (.. ": { " (commasep out #(comp.type $1 scope)) " }") "")
-                       argdefs (commasep argpairs #(.. (scope:addlocal $1.name) " : " (comp.type $1.type scope)))]
-                    (block (.. "terra (" argdefs ")" rettyp) stmts :end scope #(comp.expr $1 scope)))))
+    (if (> (length stmts) 0)
+        (scope:with #(let [(in out) (split-arglist arglist)
+                        argpairs (fcollect [i 1 (length in) 2] {:name (. in i) :type (. in (+ i 1))})
+                        rettyp  (if out (.. ": { " (commasep out #(comp.type $1 scope)) " }") "")
+                        argdefs (commasep argpairs #(.. (scope:addlocal $1.name) " : " (comp.type $1.type scope)))]
+                        (block (.. "terra (" argdefs ")" rettyp) stmts :end scope #(comp.expr $1 scope))))
+        (.. "(function () local terra anonfn :: " ((. type-constructors "->") arglist scope) " return anonfn end)()")))
 
 (fn forms.return [vals scope] (.. "return " (commasep vals #(comp.expr $1 scope))))
 
@@ -220,6 +222,22 @@
 (tset forms ":" (fn [[obj field & args] scope]
     (.. (comp.expr obj scope) ":[" (scope:expr field) "](" (commasep args #(comp.expr $1 scope)) ")")))
 
+(fn forms.if [params scope]
+    (let [has-else? (= (% (length params) 2) 1)
+          ilast (if has-else? (length params) (- (length params) 1))
+          ielse (when has-else? ilast)
+          clauses (fcollect [i 1 (length params) 2]
+                    (if (= i ielse) 
+                        {:pre (indent :else scope)
+                         :post :end
+                         :clause (. params i)}
+                        {:pre (.. (if (= i 1) :if (indent :elseif scope)) " " (comp.expr (. params i) scope) " then")
+                         :post (if (= i ilast) :end "")
+                         :clause (. params (+ i 1))}))
+          blocks (icollect [_ clause (ipairs clauses)]
+                    (scope:with #(block clause.pre [clause.clause] clause.post scope #(comp.expr $1 scope))))]
+        (table.concat blocks "\n")))
+
 (fn comp.quote [stmts scope]
     (if (= (length stmts) 1) (.. "`(" (comp.expr (. stmts 1) scope) ")")
         (.. "quote\n" (commasep stmts #(comp.expr $1 scope)) "\nend")))