Add more error messages

source/compiler/compiler.go

@@ -1325,7 +1325,7 @@ func (cp *Compiler) compileForExpression(node *ast.ForExpression, ctxt Context)
 		for i, pair := range indexSig {
 			_, exists := newEnv.GetVar(pair.VarName)
 			if exists {
-				cp.P.Throw("comp/for/index/exists", node.Initializer.GetToken())
+				cp.P.Throw("comp/for/exists/index", node.Initializer.GetToken(), pair.VarName)
 				return altType(values.COMPILE_TIME_ERROR)
 			}
 			cp.Reserve(values.UNDEFINED_TYPE, nil, tok)
@@ -1529,7 +1529,7 @@ func (cp *Compiler) resolveBreaksWithValue() {
 // Compile a `continue` in a `for loop`.
 func (cp *Compiler) emitContinue(tok *token.Token) {
 	if len(cp.forData) == 0 {
-		cp.P.Throw("comp/for/continue", tok)
+		cp.P.Throw("comp/continue", tok)
 		return
 	}
 	cp.addToForData(cp.vmContinue())
@@ -1704,7 +1704,7 @@ func (cp *Compiler) CompileGivenBlock(given ast.Node, ctxt Context) {
 		for _, pair := range lhsSig {
 			_, exists := ctxt.Env.GetVar(pair.VarName)
 			if exists {
-				cp.P.Throw("comp/given/exists", chunk.GetToken())
+				cp.P.Throw("comp/given/exists", chunk.GetToken(), pair.VarName)
 				return
 			}
 			nameToNode[pair.VarName] = assEx

source/err/errorfile.go

@@ -285,6 +285,16 @@ var ErrorCreatorMap = map[string]ErrorCreator{
 		},
 	},
 
+	"comp/continue": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "'continue' outside of 'for' loop"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "The 'continue' keyword really has no meaning outside of a 'for' loop, " +
+			       "since what it means is \"continue the 'for' loop we're in without changing the bound variables\"."
+		},
+	},
+
 	"comp/error/arg": {
 		Message: func(tok *token.Token, args ...any) string {
 			return "expression can only return error"
@@ -340,40 +350,6 @@ var ErrorCreatorMap = map[string]ErrorCreator{
 		},
 	},
 
-	"comp/given/cycle": {
-		Message: func(tok *token.Token, args ...any) string {
-			cycle := args[0].([]string)
-			var description string
-			if len(cycle) == 1 {
-				description = emph(cycle[0]) + " is defined in terms of itself"
-			} else {
-				sep := ""
-				for _, name := range cycle {
-					description = description + sep + emph(name)
-					if sep == "" {
-						sep = " is defined in terms of "
-					} else {
-						sep = ", which is defined in terms of "
-					}
-				}
-				description = description + ", which is defined in terms of " + emph(cycle[0])
-			}
-			return description + " in " + emph("given") + " block"
-		},
-		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
-			return "It isn't possible to define variables in terms of each other because how would that even work?"
-		},
-	},
-
-	"comp/log/close": {
-		Message: func(tok *token.Token, args ...any) string {
-			return "unclosed " + emph("|") + " in logging expression"
-		},
-		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
-			return "Pipefish interprets " + emph("| <expression> |") + " in a logging expression as meaning that the expression should be evaluated and inserted into the string. It therefore expects the " + emph("|") + " symbols to come in matching pairs."
-		},
-	},
-
 	"comp/fcis": {
 		Message: func(tok *token.Token, args ...any) string {
 			return "imperative code in " + emph("def") + " section"
@@ -432,6 +408,7 @@ var ErrorCreatorMap = map[string]ErrorCreator{
 		},
 	},
 
+
 	"comp/for/bound/present": {
 		Message: func(tok *token.Token, args ...any) string {
 			return "loop has no bound variables"
@@ -442,7 +419,7 @@ var ErrorCreatorMap = map[string]ErrorCreator{
 		},
 	},
 
-	"comp/for/exists/key": {
+	"comp/for/exists/index": {
 		Message: func(tok *token.Token, args ...any) string {
 			return "reassigning to variable " + emph(args[0])
 		},
@@ -451,6 +428,14 @@ var ErrorCreatorMap = map[string]ErrorCreator{
 		},
 	},
 
+	"comp/for/exists/key": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "reassigning to variable " + emph(args[0])
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "The index variables of a 'for' loop cannot have already been declared in the scope."
+		},
+	},
 
 	"comp/for/exists/value": {
 		Message: func(tok *token.Token, args ...any) string {
@@ -461,6 +446,109 @@ var ErrorCreatorMap = map[string]ErrorCreator{
 		},
 	},
 
+	"comp/for/range/a": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "malformed assignment of range"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "Pipefish expect the range of a 'for' loop to be assigned to a pair of " +
+			       "index variables separated by a '::' operator."
+		},
+	},
+
+	"comp/for/range/b": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "malformed assignment of range"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "Pipefish expect the range of a 'for' loop to be assigned to a pair of " +
+			       "index variables separated by a '::' operator."
+		},
+	},
+
+	"comp/for/range/c": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "malformed assignment of range"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "Pipefish expect the range of a 'for' loop to be assigned to a pair of " +
+			       "index variables separated by a '::' operator."
+		},
+	},
+
+	"comp/for/range/discard": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "discarding both key and value of range"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "Pipefish currently doesn't let you do this. It may be allowed in later " +
+			       "versions, since there is a marginal use-case."       // TODO.
+		},
+	},
+
+	"comp/for/range/types": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "ranging over invalid type"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "The argument of 'range' should be a type you can in fact range over, such as a list or a set."
+		},
+	},
+
+	"comp/given/assign": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "malformed expression in 'given' block"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "Pipefish was expecting either a function declaration or an assignment, and " +
+			       "this is neither."
+		},
+	},
+
+	"comp/given/cycle": {
+		Message: func(tok *token.Token, args ...any) string {
+			cycle := args[0].([]string)
+			var description string
+			if len(cycle) == 1 {
+				description = emph(cycle[0]) + " is defined in terms of itself"
+			} else {
+				sep := ""
+				for _, name := range cycle {
+					description = description + sep + emph(name)
+					if sep == "" {
+						sep = " is defined in terms of "
+					} else {
+						sep = ", which is defined in terms of "
+					}
+				}
+				description = description + ", which is defined in terms of " + emph(cycle[0])
+			}
+			return description + " in " + emph("given") + " block"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "It isn't possible to define variables in terms of each other because how would that even work?"
+		},
+	},
+
+	"comp/given/exists": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "variable " + emph(args[0]) + " already exists"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "Pipefish doesn't allow the variables declared in a 'given' block " +
+			"to \"shadow\" existing variables."
+		},
+	},
+
+	"comp/given/redeclared": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "variable " + emph(args[0]) + " defined twice"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "You've tried to define the same variable twice on the left-hand side of the same assignment."
+		},
+	},
+
 	"comp/global/global": {
 		Message: func(tok *token.Token, args ...any) string {
 			return "identifier " + emph(tok.Literal) + " doesn't identify a global variable"
@@ -614,6 +702,15 @@ var ErrorCreatorMap = map[string]ErrorCreator{
 		},
 	},
 
+	"comp/log/close": {
+		Message: func(tok *token.Token, args ...any) string {
+			return "unclosed " + emph("|") + " in logging expression"
+		},
+		Explanation: func(errors Errors, pos int, tok *token.Token, args ...any) string {
+			return "Pipefish interprets " + emph("| <expression> |") + " in a logging expression as meaning that the expression should be evaluated and inserted into the string. It therefore expects the " + emph("|") + " symbols to come in matching pairs."
+		},
+	},
+
 	"comp/loop/body": {
 		Message: func(tok *token.Token, args ...any) string {
 			return "trying to return a value from an imperative loop"

source/vm/descriptors.go

@@ -98,7 +98,9 @@ func (vm *Vm) toString(v values.Value, flavor descriptionFlavor) string {
 			return "nil error"
 		}
 		ob := v.V.(*err.Error)
-		ob = err.CreateErr(ob.ErrorId, ob.Token, ob.Args...)
+		if ob.ErrorId != "vm/user" {
+			ob = err.CreateErr(ob.ErrorId, ob.Token, ob.Args...)
+		}
 		return text.Pretty(text.RT_ERROR+ob.Message+text.DescribePos(ob.Token)+".", 0, 80)
 	case values.FLOAT:
 		return strconv.FormatFloat(v.V.(float64), 'f', 8, 64)

source/vm/vm.go

@@ -873,7 +873,7 @@ loop:
 		case Logy:
 			vm.logging = true
 		case Mker:
-			vm.Mem[args[0]] = values.Value{values.ERROR, &err.Error{ErrorId: "eval/user", Message: vm.Mem[args[1]].V.(string), Token: vm.Tokens[args[2]]}}
+			vm.Mem[args[0]] = values.Value{values.ERROR, &err.Error{ErrorId: "vm/user", Message: vm.Mem[args[1]].V.(string), Token: vm.Tokens[args[2]]}}
 		case Mkfn:
 			lf := vm.LambdaFactories[args[1]]
 			newLambda := *lf.Model