From 59fb2c02e08b9bf577f2dedfabd290cb6e00e016 Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Fri, 1 Nov 2024 10:01:20 -0700
Subject: Some ideas on functions

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 chapter17/README.md | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

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index e0e71539..bedce38b 100644
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@@ -1,3 +1,62 @@
 # Chapter 17: Functions
 
+Some thinking on function syntax:
 
+Function Types:
+```
+{ argtype, argtype, ... -> rettype }
+```
+
+Leading `{` character denotes the start of a function or function type.
+
+Functions are normal variables and assigned the same way:
+
+```functiontype var = function-typed-expr```
+
+Functions themselves using the same syntax with as types, but filled in:
+
+```
+{ int x, int y ->
+  sqrt(x*x+y*y);
+}
+```
+
+Used in a declaration statement:
+```
+// TYPE        VAR  =   EXPR
+{flt,flt->flt} dist = { flt x, flt y ->
+  sqrt(x*x+y*y);
+}
+```
+
+Because it gets clunky to write the function type, and because it can be
+directly inferred from forwards-flow analysis (not even HM) which we're already
+doing at parse-time, we add a new variable declaration syntax: "var" - for
+auto-inferring variable types.  Not allowed in function headers.
+```
+var dist = { flt x, flt y -> sqrt(x*x*,y*y); }
+```
+
+`var` can be used for normal variables as well:
+
+```
+// Newtons approximation to the square root
+var sqrt = { flt x ->
+    var guess = x*x/2;
+    while( 1 ) {
+        var next = (x/guess + guess)/2;
+        if( next == guess ) break;
+        guess = next;
+    }
+    guess;
+}
+```
+
+When inferring pointer types, it will use the `glb` of the initial expression
+type, which may not be what you want:
+
+```
+struct LLI { LLI? next; int i; };
+var head = LLI(); // Want this declared not-null, but GLB will allow null
+head = null;      // Allowed
+```
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