]> ocean-lang.org Git - ocean/blobdiff - csrc/oceani.mdc
oceani: detect and report tails on numbers and strings.
[ocean] / csrc / oceani.mdc
index 9abd338e0d92db27cc181e280788f54dd179dde8..ebb69ade3d2a32f40e0e3666ed6416cf8d2cc4e9 100644 (file)
@@ -109,6 +109,8 @@ option.
        ## ast
        struct parse_context {
                struct token_config config;
+               char *file_name;
+               int parse_error;
                ## parse context
        };
 
@@ -197,6 +199,7 @@ option.
                        fprintf(stderr, "oceani: cannot open %s\n", argv[optind]);
                        exit(1);
                }
+               context.file_name = argv[optind];
                len = lseek(fd, 0, 2);
                file = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
                s = code_extract(file, file+len, NULL);
@@ -224,11 +227,15 @@ option.
                } else
                        prog = parse_oceani(s->code, &context.config,
                                    dotrace ? stderr : NULL);
+               if (!prog) {
+                       fprintf(stderr, "oceani: fatal parser error.\n");
+                       context.parse_error = 1;
+               }
                if (prog && doprint)
                        print_exec(*prog, 0, brackets);
-               if (prog && doexec) {
+               if (prog && doexec && !context.parse_error) {
                        if (!analyse_prog(*prog, &context)) {
-                               fprintf(stderr, "oceani: type error in program\n");
+                               fprintf(stderr, "oceani: type error in program - not running.\n");
                                exit(1);
                        }
                        interp_prog(*prog, argv+optind+1);
@@ -244,7 +251,7 @@ option.
                        s = t;
                }
                ## free context
-               exit(0);
+               exit(context.parse_error ? 1 : 0);
        }
 
 ### Analysis
@@ -296,9 +303,84 @@ type that gets passed around comprises a type (`enum vtype`) and a
 flag to indicate that `Vbool` is also permitted.
 
 As there are, as yet, no distinct types that are compatible, there
-isn't much subtlety in the analysis.  When we hav distinct number
+isn't much subtlety in the analysis.  When we have distinct number
 types, this will become more interesting.
 
+#### Error reporting
+
+When analysis discovers an inconsistency it needs to report an error;
+just refusing to run the code esure that the error doesn't cascade,
+but by itself it isn't very useful.  A clear understand of the sort of
+error message that are useful will help guide the process of analysis.
+
+At a simplistic level, the only sort of error that type analysis can
+report is that the type of some construct doesn't match a contextual
+requirement.  For example, in `4 + "hello"` the addition provides a
+contextual requirement for numbers, but `"hello"` is not a number.  In
+this particular example no further information is needed as the types
+are obvious from local information.  When a variable is involved that
+isn't the case.  It may be helpful to explain why the variable has a
+particular type, by indicating the location where the type was set,
+whether by declaration or usage.
+
+Using a recursive-descent analysis we can easily detect a problem at
+multiple locations. In "`hello:= "there"; 4 + hello`" the addition
+will detect that one argument is not a number and the usage of `hello`
+will detect that a number was wanted, but not provided.  In this
+(early) version of the language, we will generate error reports at
+multiple locations, to the use of `hello` will report an error and
+explain were the value was set, and the addition will report an error
+and say why numbers are needed.  To be able to report locations for
+errors, each language element will need to record a file location
+(line and column) and each variable will need to record the language
+element where its type was set.  For now we will assume that each line
+of an error message indicates one location in the file, and up to 2
+types.  So we provide a `printf`-like function which takes a format, a
+language (a `struct exec` which has not yet been introduced), and 2
+types. "`$1`" reports the first type, "`$2`" reports the second.  We
+will need a function to print the location, once we know how that is
+stored.
+
+###### forward decls
+
+       static void fput_loc(struct exec *loc, FILE *f);
+
+###### core functions
+
+       static void type_err(struct parse_context *c,
+                            char *fmt, struct exec *loc,
+                            enum vtype t1, enum vtype t2)
+       {
+               fprintf(stderr, "%s:", c->file_name);
+               fput_loc(loc, stderr);
+               for (; *fmt ; fmt++) {
+                       if (*fmt != '%') {
+                               fputc(*fmt, stderr);
+                               continue;
+                       }
+                       fmt++;
+                       switch (*fmt) {
+                       case '%': fputc(*fmt, stderr); break;
+                       default: fputc('?', stderr); break;
+                       case '1':
+                               fputs(vtype_names[t1], stderr);
+                               break;
+                       case '2':
+                               fputs(vtype_names[t2], stderr);
+                               break;
+                       ## format cases
+                       }
+               }
+               fputs("\n", stderr);
+               c->parse_error = 1;
+       }
+
+       static void tok_err(struct parse_context *c, char *fmt, struct token *t)
+       {
+               fprintf(stderr, "%s:%d:%d: %s\n", c->file_name, t->line, t->col, fmt);
+               c->parse_error = 1;
+       }
+
 ## Data Structures
 
 One last introductory step before detailing the language elements and
@@ -355,6 +437,9 @@ to parse each type from a string.
                char tail[2];
        };
 
+       char *vtype_names[] = {"nolabel", "unknown", "none", "string",
+                              "number", "Boolean", "label"};
+
 ###### ast functions
        static void free_value(struct value v)
        {
@@ -584,6 +669,8 @@ cannot nest, so a declaration while a name is in-scope is an error.
                struct variable *previous;
                struct value val;
                struct binding *name;
+               struct exec *where_decl;// where name was declared
+               struct exec *where_set; // where type was set
                ## variable fields
        };
 
@@ -815,7 +902,7 @@ all pending-scope variables become conditionally scoped.
 
                switch (v ? v->scope : OutScope) {
                case InScope:
-                       /* Signal error ... once I build error signalling support */
+                       /* Caller will report the error */
                        return NULL;
                case CondScope:
                        for (;
@@ -960,9 +1047,16 @@ subclasses, and to access these we need to be able to `cast` the
                if (__mptr && *__mptr != X##structname) abort();                \
                (struct structname *)( (char *)__mptr);})
 
-       #define new(structname) ({                      \
+       #define new(structname) ({                                              \
                struct structname *__ptr = ((struct structname *)calloc(1,sizeof(struct structname))); \
-               __ptr->type = X##structname;            \
+               __ptr->type = X##structname;                                            \
+               __ptr->line = -1; __ptr->column = -1;                                   \
+               __ptr;})
+
+       #define new_pos(structname, token) ({                                           \
+               struct structname *__ptr = ((struct structname *)calloc(1,sizeof(struct structname))); \
+               __ptr->type = X##structname;                                            \
+               __ptr->line = token.line; __ptr->column = token.col;                    \
                __ptr;})
 
 ###### ast
@@ -972,6 +1066,7 @@ subclasses, and to access these we need to be able to `cast` the
        };
        struct exec {
                enum exec_types type;
+               int line, column;
        };
        struct binode {
                struct exec;
@@ -981,6 +1076,25 @@ subclasses, and to access these we need to be able to `cast` the
                struct exec *left, *right;
        };
 
+###### ast functions
+
+       static int __fput_loc(struct exec *loc, FILE *f)
+       {
+               if (loc->line >= 0) {
+                       fprintf(f, "%d:%d: ", loc->line, loc->column);
+                       return 1;
+               }
+               if (loc->type == Xbinode)
+                       return __fput_loc(cast(binode,loc)->left, f) ||
+                              __fput_loc(cast(binode,loc)->right, f);
+               return 0;
+       }
+       static void fput_loc(struct exec *loc, FILE *f)
+       {
+               if (!__fput_loc(loc, f))
+                       fprintf(f, "??:??: ");
+       }
+
 Each different type of `exec` node needs a number of functions
 defined, a bit like methods.  We must be able to be able to free it,
 print it, analyse it and execute it.  Once we have specific `exec`
@@ -1048,6 +1162,8 @@ also want to know what sort of bracketing to use.
 
        static void print_exec(struct exec *e, int indent, int bracket)
        {
+               if (!e)
+                       return;
                switch (e->type) {
                case Xbinode:
                        print_binode(cast(binode, e), indent, bracket); break;
@@ -1073,7 +1189,7 @@ remains unchanged at `1`, then no more propagation is needed.
 
 ###### core functions
 
-       static enum vtype propagate_types(struct exec *prog, int *ok,
+       static enum vtype propagate_types(struct exec *prog, struct parse_context *c, int *ok,
                                          enum vtype type, int bool_permitted)
        {
                enum vtype t;
@@ -1157,30 +1273,39 @@ an executable.
 
        $*val
        Value ->  True ${
-                       $0 = new(val);
+                       $0 = new_pos(val, $1);
                        $0->val.vtype = Vbool;
                        $0->val.bool = 1;
                        }$
                | False ${
-                       $0 = new(val);
+                       $0 = new_pos(val, $1);
                        $0->val.vtype = Vbool;
                        $0->val.bool = 0;
                        }$
                | NUMBER ${
-                       $0 = new(val);
+                       $0 = new_pos(val, $1);
                        $0->val.vtype = Vnum;
                        if (number_parse($0->val.num, $0->val.tail, $1.txt) == 0)
                                mpq_init($0->val.num);
+                               if ($0->val.tail[0])
+                                       tok_err(config2context(config), "error: unsupported number suffix.",
+                                               &$1);
                        }$
                | STRING ${
-                       $0 = new(val);
+                       $0 = new_pos(val, $1);
                        $0->val.vtype = Vstr;
                        string_parse(&$1, '\\', &$0->val.str, $0->val.tail);
+                       if ($0->val.tail[0])
+                               tok_err(config2context(config), "error: unsupported string suffix.",
+                                       &$1);
                        }$
                | MULTI_STRING ${
-                       $0 = new(val);
+                       $0 = new_pos(val, $1);
                        $0->val.vtype = Vstr;
                        string_parse(&$1, '\\', &$0->val.str, $0->val.tail);
+                       if ($0->val.tail[0])
+                               tok_err(config2context(config), "error: unsupported string suffix.",
+                                       &$1);
                        }$
 
 ###### print exec cases
@@ -1199,8 +1324,11 @@ an executable.
                case Xval:
                {
                        struct val *val = cast(val, prog);
-                       if (!vtype_compat(type, val->val.vtype, bool_permitted))
+                       if (!vtype_compat(type, val->val.vtype, bool_permitted)) {
+                               type_err(c, "error: expected %1 found %2",
+                                          prog, type, val->val.vtype);
                                *ok = 0;
+                       }
                        return val->val.vtype;
                }
 
@@ -1264,25 +1392,47 @@ link to find the primary instance.
        $*var
        VariableDecl -> IDENTIFIER := ${ {
                struct variable *v = var_decl(config2context(config), $1.txt);
-               $0 = new(var);
+               $0 = new_pos(var, $1);
                $0->var = v;
+               if (v)
+                       v->where_decl = $0;
+               else {
+                       v = var_ref(config2context(config), $1.txt);
+                       $0->var = v;
+                       type_err(config2context(config), "error: variable '%v' redeclared",
+                                $0, Vnone, Vnone);
+                       type_err(config2context(config), "info: this is where '%v' was first declared",
+                                v->where_decl, Vnone, Vnone);
+               }
        } }$
            | IDENTIFIER ::= ${ {
                struct variable *v = var_decl(config2context(config), $1.txt);
-               v->constant = 1;
-               $0 = new(var);
+               $0 = new_pos(var, $1);
                $0->var = v;
+               if (v) {
+                       v->where_decl = $0;
+                       v->constant = 1;
+               } else {
+                       v = var_ref(config2context(config), $1.txt);
+                       $0->var = v;
+                       type_err(config2context(config), "error: variable '%v' redeclared",
+                                $0, Vnone, Vnone);
+                       type_err(config2context(config), "info: this is where '%v' was first declared",
+                                v->where_decl, Vnone, Vnone);
+               }
        } }$
 
        Variable -> IDENTIFIER ${ {
                struct variable *v = var_ref(config2context(config), $1.txt);
+               $0 = new_pos(var, $1);
                if (v == NULL) {
                        /* This might be a label - allocate a var just in case */
                        v = var_decl(config2context(config), $1.txt);
-                       if (v)
+                       if (v) {
                                val_init(&v->val, Vlabel);
+                               v->where_set = $0;
+                       }
                }
-               $0 = new(var);
                $0->var = v;
        } }$
 
@@ -1297,6 +1447,19 @@ link to find the primary instance.
                break;
        }
 
+###### format cases
+       case 'v':
+               if (loc->type == Xvar) {
+                       struct var *v = cast(var, loc);
+                       if (v->var) {
+                               struct binding *b = v->var->name;
+                               fprintf(stderr, "%.*s", b->name.len, b->name.txt);
+                       } else
+                               fputs("???", stderr);
+               } else
+                       fputs("NOTVAR", stderr);
+               break;
+
 ###### propagate exec cases
 
        case Xvar:
@@ -1304,6 +1467,7 @@ link to find the primary instance.
                struct var *var = cast(var, prog);
                struct variable *v = var->var;
                if (!v) {
+                       type_err(c, "%d:BUG: no variable!!", prog, Vnone, Vnone);
                        *ok = 0;
                        return Vnone;
                }
@@ -1312,12 +1476,18 @@ link to find the primary instance.
                if (v->val.vtype == Vunknown) {
                        if (type > Vunknown && *ok != 0) {
                                val_init(&v->val, type);
+                               v->where_set = prog;
                                *ok = 2;
                        }
                        return type;
                }
-               if (!vtype_compat(type, v->val.vtype, bool_permitted))
+               if (!vtype_compat(type, v->val.vtype, bool_permitted)) {
+                       type_err(c, "error: expected %1 but variable '%v' is %2", prog,
+                                type, v->val.vtype);
+                       type_err(c, "info: this is where '%v' was set to %1", v->where_set,
+                                v->val.vtype, Vnone);
                        *ok = 0;
+               }
                if (type <= Vunknown)
                        return v->val.vtype;
                return type;
@@ -1360,28 +1530,31 @@ and `BFact`s.
 
 ####### Grammar
 
-       $*binode
-       Expression -> Expression or BTerm ${
-                       $0 = new(binode);
-                       $0->op = Or;
-                       $0->left = $<1;
-                       $0->right = $<3;
-               }$
+       $*exec
+       Expression -> Expression or BTerm ${ {
+                       struct binode *b = new(binode);
+                       b->op = Or;
+                       b->left = $<1;
+                       b->right = $<3;
+                       $0 = b;
+               } }$
                | BTerm ${ $0 = $<1; }$
 
-       BTerm -> BTerm and BFact ${
-                       $0 = new(binode);
-                       $0->op = And;
-                       $0->left = $<1;
-                       $0->right = $<3;
-               }$
+       BTerm -> BTerm and BFact ${ {
+                       struct binode *b = new(binode);
+                       b->op = And;
+                       b->left = $<1;
+                       b->right = $<3;
+                       $0 = b;
+               } }$
                | BFact ${ $0 = $<1; }$
 
-       BFact -> not BFact ${
-                       $0 = new(binode);
-                       $0->op = Not;
-                       $0->right = $<2;
-                       }$
+       BFact -> not BFact ${ {
+                       struct binode *b = new(binode);
+                       b->op = Not;
+                       b->right = $<2;
+                       $0 = b;
+               } }$
                ## other BFact
 
 ###### print binode cases
@@ -1405,10 +1578,13 @@ and `BFact`s.
        case Or:
        case Not:
                /* both must be Vbool, result is Vbool */
-               propagate_types(b->left, ok, Vbool, 0);
-               propagate_types(b->right, ok, Vbool, 0);
-               if (type != Vbool && type > Vunknown)
+               propagate_types(b->left, c, ok, Vbool, 0);
+               propagate_types(b->right, c, ok, Vbool, 0);
+               if (type != Vbool && type > Vunknown) {
+                       type_err(c, "error: %1 operation found where %2 expected", prog,
+                                  Vbool, type);
                        *ok = 0;
+               }
                return Vbool;
 
 ###### interp binode cases
@@ -1458,12 +1634,13 @@ expression operator.
        NEql,
 
 ###### other BFact
-       | Expr CMPop Expr ${
-                       $0 = new(binode);
-                       $0->op = $2.op;
-                       $0->left = $<1;
-                       $0->right = $<3;
-               }$
+       | Expr CMPop Expr ${ {
+                       struct binode *b = new(binode);
+                       b->op = $2.op;
+                       b->left = $<1;
+                       b->right = $<3;
+                       $0 = b;
+       } }$
        | Expr ${ $0 = $<1; }$
 
 ###### Grammar
@@ -1505,16 +1682,19 @@ expression operator.
        case Eql:
        case NEql:
                /* Both must match but not labels, result is Vbool */
-               t = propagate_types(b->left, ok, Vnolabel, 0);
+               t = propagate_types(b->left, c, ok, Vnolabel, 0);
                if (t > Vunknown)
-                       propagate_types(b->right, ok, t, 0);
+                       propagate_types(b->right, c, ok, t, 0);
                else {
-                       t = propagate_types(b->right, ok, Vnolabel, 0);
+                       t = propagate_types(b->right, c, ok, Vnolabel, 0);
                        if (t > Vunknown)
-                               t = propagate_types(b->left, ok, t, 0);
+                               t = propagate_types(b->left, c, ok, t, 0);
                }
-               if (!vtype_compat(type, Vbool, 0))
+               if (!vtype_compat(type, Vbool, 0)) {
+                       type_err(c, "error: Comparison returns %1 but %2 expected", prog,
+                                   Vbool, type);
                        *ok = 0;
+               }
                return Vbool;
 
 ###### interp binode cases
@@ -1565,35 +1745,39 @@ precedence is handled better I might be able to discard this.
 
 ###### Grammar
 
-       $*binode
-       Expr -> Expr Eop Term ${
-                       $0 = new(binode);
-                       $0->op = $2.op;
-                       $0->left = $<1;
-                       $0->right = $<3;
-               }$
+       $*exec
+       Expr -> Expr Eop Term ${ {
+                       struct binode *b = new(binode);
+                       b->op = $2.op;
+                       b->left = $<1;
+                       b->right = $<3;
+                       $0 = b;
+               } }$
                | Term ${ $0 = $<1; }$
 
-       Term -> Term Top Factor ${
-                       $0 = new(binode);
-                       $0->op = $2.op;
-                       $0->left = $<1;
-                       $0->right = $<3;
-               }$
+       Term -> Term Top Factor ${ {
+                       struct binode *b = new(binode);
+                       b->op = $2.op;
+                       b->left = $<1;
+                       b->right = $<3;
+                       $0 = b;
+               } }$
                | Factor ${ $0 = $<1; }$
 
-       Factor -> ( Expression ) ${
-                       $0 = new(binode);
-                       $0->op = Bracket;
-                       $0->right = $<2;
-               }$
-               | Uop Factor ${
-                       $0 = new(binode);
-                       $0->op = $1.op;
-                       $0->right = $<2;
-               }$
-               | Value ${ $0 = (struct binode *)$<1; }$
-               | Variable ${ $0 = (struct binode *)$<1; }$
+       Factor -> ( Expression ) ${ {
+                       struct binode *b = new_pos(binode, $1);
+                       b->op = Bracket;
+                       b->right = $<2;
+                       $0 = b;
+               } }$
+               | Uop Factor ${ {
+                       struct binode *b = new(binode);
+                       b->op = $1.op;
+                       b->right = $<2;
+                       $0 = b;
+               } }$
+               | Value ${ $0 = $<1; }$
+               | Variable ${ $0 = $<1; }$
 
        $eop
        Eop ->    + ${ $0.op = Plus; }$
@@ -1647,22 +1831,28 @@ precedence is handled better I might be able to discard this.
        case Negate:
                /* as propagate_types ignores a NULL,
                 * unary ops fit here too */
-               propagate_types(b->left, ok, Vnum, 0);
-               propagate_types(b->right, ok, Vnum, 0);
-               if (!vtype_compat(type, Vnum, 0))
+               propagate_types(b->left, c, ok, Vnum, 0);
+               propagate_types(b->right, c, ok, Vnum, 0);
+               if (!vtype_compat(type, Vnum, 0)) {
+                       type_err(c, "error: Arithmetic returns %1 but %2 expected", prog,
+                                  Vnum, type);
                        *ok = 0;
+               }
                return Vnum;
 
        case Concat:
                /* both must be Vstr, result is Vstr */
-               propagate_types(b->left, ok, Vstr, 0);
-               propagate_types(b->right, ok, Vstr, 0);
-               if (!vtype_compat(type, Vstr, 0))
+               propagate_types(b->left, c, ok, Vstr, 0);
+               propagate_types(b->right, c, ok, Vstr, 0);
+               if (!vtype_compat(type, Vstr, 0)) {
+                       type_err(c, "error: Concat returns %1 but %2 expected", prog,
+                                  Vstr, type);
                        *ok = 0;
+               }
                return Vstr;
 
        case Bracket:
-               return propagate_types(b->right, ok, type, 0);
+               return propagate_types(b->right, c, ok, type, 0);
 
 ###### interp binode cases
 
@@ -1847,7 +2037,7 @@ list.
        case Block:
        {
                /* If any statement returns something other then Vnone
-                * then all such must return same type.
+                * or Vbool then all such must return same type.
                 * As each statement may be Vnone or something else,
                 * we must always pass Vunknown down, otherwise an incorrect
                 * error might occur.  We never return Vnone unless it is
@@ -1856,14 +2046,17 @@ list.
                struct binode *e;
 
                for (e = b; e; e = cast(binode, e->right)) {
-                       t = propagate_types(e->left, ok, Vunknown, bool_permitted);
+                       t = propagate_types(e->left, c, ok, Vunknown, bool_permitted);
                        if (bool_permitted && t == Vbool)
                                t = Vunknown;
-                       if (t != Vunknown && t != Vnone) {
+                       if (t != Vunknown && t != Vnone && t != Vbool) {
                                if (type == Vunknown)
                                        type = t;
-                               else if (t != type)
+                               else if (t != type) {
+                                       type_err(c, "error: expected %1, found %2",
+                                                e->left, type, t);
                                        *ok = 0;
+                               }
                        }
                }
                return type;
@@ -1946,8 +2139,8 @@ same solution.
 
        case Print:
                /* don't care but all must be consistent */
-               propagate_types(b->left, ok, Vnolabel, 0);
-               propagate_types(b->right, ok, Vnolabel, 0);
+               propagate_types(b->left, c, ok, Vnolabel, 0);
+               propagate_types(b->right, c, ok, Vnolabel, 0);
                break;
 
 ###### interp binode cases
@@ -2034,13 +2227,16 @@ it is declared, and error will be raised as the name is created as
        case Assign:
        case Declare:
                /* Both must match and not be labels, result is Vnone */
-               t = propagate_types(b->left, ok, Vnolabel, 0);
-               if (t > Vunknown)
-                       propagate_types(b->right, ok, t, 0);
-               else {
-                       t = propagate_types(b->right, ok, Vnolabel, 0);
+               t = propagate_types(b->left, c, ok, Vnolabel, 0);
+               if (t > Vunknown) {
+                       if (propagate_types(b->right, c, ok, t, 0) != t)
+                               if (b->left->type == Xvar)
+                                       type_err(c, "info: variable '%v' was set as %1 here.",
+                                                cast(var, b->left)->var->where_set, t, Vnone);
+               } else {
+                       t = propagate_types(b->right, c, ok, Vnolabel, 0);
                        if (t > Vunknown)
-                               t = propagate_types(b->left, ok, t, 0);
+                               propagate_types(b->left, c, ok, t, 0);
                }
                return Vnone;
 
@@ -2073,7 +2269,7 @@ function.
 
 ###### SimpleStatement Grammar
        | use Expression ${
-               $0 = new(binode);
+               $0 = new_pos(binode, $1);
                $0->op = Use;
                $0->right = $<2;
        }$
@@ -2091,7 +2287,7 @@ function.
 
        case Use:
                /* result matches value */
-               return propagate_types(b->right, ok, type, 0);
+               return propagate_types(b->right, c, ok, type, 0);
 
 ###### interp binode cases
 
@@ -2479,51 +2675,51 @@ defined.
                // elsepart, casepart->action must match there return type
                // expected of this statement.
                struct cond_statement *cs = cast(cond_statement, prog);
-               struct casepart *c;
+               struct casepart *cp;
 
-               t = propagate_types(cs->forpart, ok, Vnone, 0);
+               t = propagate_types(cs->forpart, c, ok, Vnone, 0);
                if (!vtype_compat(Vnone, t, 0))
                        *ok = 0;
-               t = propagate_types(cs->dopart, ok, Vnone, 0);
+               t = propagate_types(cs->dopart, c, ok, Vnone, 0);
                if (!vtype_compat(Vnone, t, 0))
                        *ok = 0;
                if (cs->dopart) {
-                       t = propagate_types(cs->thenpart, ok, Vnone, 0);
+                       t = propagate_types(cs->thenpart, c, ok, Vnone, 0);
                        if (!vtype_compat(Vnone, t, 0))
                                *ok = 0;
                }
                if (cs->casepart == NULL)
-                       propagate_types(cs->condpart, ok, Vbool, 0);
+                       propagate_types(cs->condpart, c, ok, Vbool, 0);
                else {
                        /* Condpart must match case values, with bool permitted */
                        t = Vunknown;
-                       for (c = cs->casepart;
-                            c && (t == Vunknown); c = c->next)
-                               t = propagate_types(c->value, ok, Vunknown, 0);
+                       for (cp = cs->casepart;
+                            cp && (t == Vunknown); cp = cp->next)
+                               t = propagate_types(cp->value, c, ok, Vunknown, 0);
                        if (t == Vunknown && cs->condpart)
-                               t = propagate_types(cs->condpart, ok, Vunknown, 1);
+                               t = propagate_types(cs->condpart, c, ok, Vunknown, 1);
                        // Now we have a type (I hope) push it down
                        if (t != Vunknown) {
-                               for (c = cs->casepart; c; c = c->next)
-                                       propagate_types(c->value, ok, t, 0);
-                               propagate_types(cs->condpart, ok, t, 1);
+                               for (cp = cs->casepart; cp; cp = cp->next)
+                                       propagate_types(cp->value, c, ok, t, 0);
+                               propagate_types(cs->condpart, c, ok, t, 1);
                        }
                }
                // (if)then, else, and case parts must return expected type.
                if (!cs->dopart && type == Vunknown)
-                       type = propagate_types(cs->thenpart, ok, Vunknown, bool_permitted);
+                       type = propagate_types(cs->thenpart, c, ok, Vunknown, bool_permitted);
                if (type == Vunknown)
-                       type = propagate_types(cs->elsepart, ok, Vunknown, bool_permitted);
-               for (c = cs->casepart;
-                    c && type == Vunknown;
-                    c = c->next)
-                       type = propagate_types(c->action, ok, Vunknown, bool_permitted);
+                       type = propagate_types(cs->elsepart, c, ok, Vunknown, bool_permitted);
+               for (cp = cs->casepart;
+                    cp && type == Vunknown;
+                    cp = cp->next)
+                       type = propagate_types(cp->action, c, ok, Vunknown, bool_permitted);
                if (type > Vunknown) {
                        if (!cs->dopart)
-                               propagate_types(cs->thenpart, ok, type, bool_permitted);
-                       propagate_types(cs->elsepart, ok, type, bool_permitted);
-                       for (c = cs->casepart; c ; c = c->next)
-                               propagate_types(c->action, ok, type, bool_permitted);
+                               propagate_types(cs->thenpart, c, ok, type, bool_permitted);
+                       propagate_types(cs->elsepart, c, ok, type, bool_permitted);
+                       for (cp = cs->casepart; cp ; cp = cp->next)
+                               propagate_types(cp->action, c, ok, type, bool_permitted);
                        return type;
                } else
                        return Vunknown;
@@ -2599,7 +2795,11 @@ analysis is a bit more interesting at this level.
                $0->right = $<4;
                var_block_close(config2context(config), CloseSequential);
                if (config2context(config)->scope_stack) abort();
-       }$
+               }$
+               | ERROR ${
+                       tok_err(config2context(config),
+                               "error: unhandled parse error.", &$1);
+               }$
 
        Varlist -> Varlist ArgDecl ${
                        $0 = new(binode);
@@ -2644,37 +2844,44 @@ analysis is a bit more interesting at this level.
                struct binode *b = cast(binode, prog);
                int ok = 1;
 
+               if (!b)
+                       return 0;
                do {
                        ok = 1;
-                       propagate_types(b->right, &ok, Vnone, 0);
+                       propagate_types(b->right, c, &ok, Vnone, 0);
                } while (ok == 2);
                if (!ok)
                        return 0;
 
                for (b = cast(binode, b->left); b; b = cast(binode, b->right)) {
                        struct var *v = cast(var, b->left);
-                       if (v->var->val.vtype == Vunknown)
+                       if (v->var->val.vtype == Vunknown) {
+                               v->var->where_set = b;
                                val_init(&v->var->val, Vstr);
+                       }
                }
                b = cast(binode, prog);
                do {
                        ok = 1;
-                       propagate_types(b->right, &ok, Vnone, 0);
+                       propagate_types(b->right, c, &ok, Vnone, 0);
                } while (ok == 2);
                if (!ok)
                        return 0;
 
                /* Make sure everything is still consistent */
-               propagate_types(b->right, &ok, Vnone, 0);
+               propagate_types(b->right, c, &ok, Vnone, 0);
                return !!ok;
        }
 
        static void interp_prog(struct exec *prog, char **argv)
        {
                struct binode *p = cast(binode, prog);
-               struct binode *al = cast(binode, p->left);
+               struct binode *al;
                struct value v;
 
+               if (!prog)
+                       return;
+               al = cast(binode, p->left);
                while (al) {
                        struct var *v = cast(var, al->left);
                        struct value *vl = &v->var->val;
@@ -2746,7 +2953,7 @@ Fibonacci, and performs a binary search for a number.
 
                for:
                        togo := 10
-                       f1 := 1; f2 := 1;
+                       f1 := 1; f2 := 1
                        print "Fibonacci:", f1,f2,
                then togo = togo - 1
                while togo > 0: