tuple destructuring

README.md

@@ -4,6 +4,18 @@ An experiment in combining [Fennel](https://fennel-lang.org) and [Terra](https:/
 ## Rationale
 Idk, seemed cool
 
+## Goals and Non-Goals
+At its core are a few a largely non-opinionated macros that directly expose the functionality
+that is only available through Terra's custom syntax. Terra code is not necessarily meant to 
+read like Fennel or have the same semantics. Early returns are fine, all variables are mutable,
+break and continue and imperative loops are the norm.
+
+Ideally it would be possible to build a much cleaner set of macros on top of these base macros.
+But the goal isn't to design a nice low-level language, it's to expose a powerful compilation 
+target. It's assumed that if you want to take advantage of Terra, it's probably because you 
+want to do horrible code-generation tricks. Hosting it inside Fennel simply makes it more 
+comfortable to do so.
+
 ## Usage
 At the top of your file, include the following:
 ```fennel
@@ -179,15 +191,25 @@ it consistently mean "create a quote" everywhere. Not sure.)
 ```fennel
 (var name initial-value)                  ; compiles to: var name = initial-value
 (var name type initial-value)             ; compiles to: var name : type = initial-value
+(var (name1 name2) val1 val2)             ; compiles to: var name1, name2 = val1, val2
+(var {name1 type1 name2 type2} val1 val2) ; compiles to: var name1 : type1, name2 : type2 = val1, val2
+(var {undefined type})                    ; compiles to: var undefined : type
 ```
 Define a local variable named `var`, and set its initial value to `initial-value`. You can
-manually specify a `type`, or you can let terra infer it from `initial-value`. There is no
-syntax for _not_ initalizing the variable on declaration.
+manually specify a `type`, or you can let terra infer it from `initial-value`. Both forms
+require `initial-value` to be provided.
+
+You can define multiple type-inferred variables at once with the `(name1 name2)` syntax, and 
+multiple explicitly-typed variables with the `{name1 type1 name2 type2}` syntax. Both of those 
+forms accept any number of initial values. If no values are provided, the variables are left 
+uninitialized. If one value is passed, Terra will treat it as a tuple destructuring. Otherwise
+you should probably pass the same number of values as names.
 
 #### assignment
 ```fennel
 (set varname value)            ; compiles to: varname = value
 (set struct.field value)       ; compiles to: struct.field = value
+(set (field1 field2) tuple)    ; compiles to: field1, field2 = tuple
 (tset struct (getfield) value) ; compiles to: struct.[getfield()] = value
 ```
 

terra.fnl

@@ -180,7 +180,15 @@
 (fn type-constructors.raw-escape [[text] scope] text)
 
 (fn forms.var [defn scope]
+    (fn rvaluelist [initvals]
+        (if (> (length initvals) 0) 
+            (.. " = " (commasep initvals #(comp.expr $1 scope))) 
+            ""))
     (case defn
+        (where [names & initvals] (list? names))
+        (.. "var " (commasep names #(scope:addlocal $1)) (rvaluelist initvals))
+        (where [nametyps & initvals] (kv-table? nametyps))
+        (.. "var " (kvcommasep nametyps #(.. (scope:addlocal $1) " : " (comp.type $2 scope))) (rvaluelist initvals))
         [name typ initval] (.. "var " (scope:addlocal name) " : " (comp.type typ scope) " = " (comp.expr initval scope)) 
         [name initval] (.. "var " (scope:addlocal name) " = " (comp.expr initval scope))))
 
@@ -214,7 +222,8 @@
 (def-infix :not= "~=")
 (fn forms.not [[expr] scope] (.. "not (" (comp.expr expr scope) ")"))
 (fn forms.set [[left right] scope]
-    (.. (comp.expr left scope) " = (" (comp.expr right scope) ")"))
+    (if (list? left) (.. (commasep left #(comp.expr $1 scope)) " = (" (comp.expr right scope) ")")
+        (.. (comp.expr left scope) " = (" (comp.expr right scope) ")")))
 (fn forms.tset [args scope]
     (let [iright (length args)
           right (. args iright)]