lang: parser, funcs: Take out the built-in history function

It's a normally named function for now, until we think of a common
package to move it into.

Hopefully this makes improving the lexer and parser easier for now. We
can consider bringing it back if needed.

examples/lang/history1.mcl

@@ -2,7 +2,7 @@ import "datetime"
 
 $dt = datetime.now()
 
-$hystvalues = {"ix0" => $dt, "ix1" => $dt{1}, "ix2" => $dt{2}, "ix3" => $dt{3},}
+$hystvalues = {"ix0" => $dt, "ix1" => history($dt, 1), "ix2" => history($dt, 2), "ix3" => history($dt, 3),}
 
 file "/tmp/mgmt/history" {
 	state => $const.res.file.state.exists,

examples/lang/hysteresis1.mcl

@@ -12,8 +12,8 @@ $threshold = 1.5	# change me if you like
 
 # simple hysteresis implementation
 $h1 = $theload > $threshold
-$h2 = $theload{1} > $threshold
+$h2 = history($theload, 1) > $threshold
-$h3 = $theload{2} > $threshold
+$h3 = history($theload, 2) > $threshold
 $unload = $h1 or $h2 or $h3
 
 virt "mgmt1" {

lang/funcs/history_func.go

@@ -27,9 +27,9 @@ import (
 )
 
 const (
-	// HistoryFuncName is the name this function is registered as. This
+	// HistoryFuncName is the name this function is registered as.
-	// starts with an underscore so that it cannot be used from the lexer.
+	// TODO: move this into a separate package
-	HistoryFuncName = "_history"
+	HistoryFuncName = "history"
 
 	// arg names...
 	historyArgNameValue = "value"

lang/parser/lexer.nex

@@ -295,40 +295,6 @@
 				panic(fmt.Sprintf("error lexing FLOAT, got: %v", err))
 			}
 		}
-/\$[a-z]+([a-z0-9_]*[a-z0-9]+)?{[0-9]+}/
-		{
-			// we have this as a single token, because otherwise the
-			// parser can get confused by the curly brackets :/
-			yylex.pos(lval) // our pos
-			s := yylex.Text()
-			s = s[1:len(s)] // remove the leading $
-			s = s[0:len(s)-1] // remove the trailing close curly
-			// XXX: nex has a bug that it gets confused by the
-			// following single curly brace. Please see:
-			// https://github.com/blynn/nex/issues/48
-			a := strings.Split(s, "{") // XXX: close match here: }
-			if len(a) != 2 {
-				panic(fmt.Sprintf("error lexing VAR_IDENTIFIER_HX: %v", a))
-			}
-			lval.str = a[0]
-			var err error
-			lval.int, err = strconv.ParseInt(a[1], 10, 64) // int64
-			if err == nil {
-				return VAR_IDENTIFIER_HX
-			} else if e := err.(*strconv.NumError); e.Err == strconv.ErrRange {
-				// this catches range errors for very large ints
-				lp := yylex.cast()
-				lp.lexerErr = &LexParseErr{
-					Err: ErrLexerIntegerOverflow,
-					Str: a[1],
-					Row: yylex.Line(),
-					Col: yylex.Column(),
-				}
-				return ERROR
-			} else {
-				panic(fmt.Sprintf("error lexing VAR_IDENTIFIER_HX, got: %v", err))
-			}
-		}
 /\$[a-z]([a-z0-9_]*[a-z0-9]+)?/
 		{
 			// an alternate pattern: /\$[a-z](|[a-z0-9_]*[a-z0-9])/

lang/parser/parser.y

@@ -86,7 +86,6 @@ func init() {
 %token ELVIS ROCKET ARROW DOT
 %token BOOL_IDENTIFIER STR_IDENTIFIER INT_IDENTIFIER FLOAT_IDENTIFIER
 %token MAP_IDENTIFIER STRUCT_IDENTIFIER VARIANT_IDENTIFIER VAR_IDENTIFIER
-%token VAR_IDENTIFIER_HX
 %token RES_IDENTIFIER
 %token IDENTIFIER CAPITALIZED_IDENTIFIER
 %token FUNC_IDENTIFIER
@@ -703,40 +702,6 @@ call:
 			},
 		}
 	}
-|	VAR_IDENTIFIER_HX
-	// get the N-th historical value, eg: $foo{3} is equivalent to: history($foo, 3)
-	{
-		posLast(yylex, yyDollar) // our pos
-		$$.expr = &ast.ExprCall{
-			Name: funcs.HistoryFuncName,
-			Args: []interfaces.Expr{
-				&ast.ExprVar{
-					Name: $1.str,
-				},
-				&ast.ExprInt{
-					V: $1.int,
-				},
-			},
-		}
-	}
-// TODO: fix conflicts with this method, and replace the above VAR_IDENTIFIER_HX
-// TODO: allow $pkg.ns.foo{4}, instead of $foo = $pkg.ns.foo ; $foo{4}
-// TODO: use this: dotted_var_identifier OPEN_BRACK INTEGER CLOSE_BRACK instead?
-//|	dotted_var_identifier OPEN_CURLY INTEGER CLOSE_CURLY
-//	{
-//		posLast(yylex, yyDollar) // our pos
-//		$$.expr = &ast.ExprCall{
-//			Name: funcs.HistoryFuncName,
-//			Args: []interfaces.Expr{
-//				&ast.ExprVar{
-//					Name: $1.str,
-//				},
-//				&ast.ExprInt{
-//					V: $3.int,
-//				},
-//			},
-//		}
-//	}
 |	expr IN expr
 	{
 		posLast(yylex, yyDollar) // our pos