Pometo Error Reference
This is the error reference document for Pometo - it should have a reference and probable cause of all errors encountered in Pometo - at compile and runtime.
CAVEAT LECTOR/Reader Beware
As the code base is very primitive errors will be subject to enormous change.
The purpose of writing these error tests early is to guide the process of putting in place error handling and reporting through the lexer, parser and then both the runtime interpreter and the compiler - and into the REPL Rappel.
To that end, don’t go mad writing error tests at this stage if your are thinking of contributing.
However the strategic aim is to have a single point of look up of error codes and where they can be generated and how they can be fixed.
Generally try and conform to the style of APL-like errors: http://microapl.com/apl_help/ch_020_030_030.htm
Index
DOMAIN ERROR
A DOMAIN ERROR is thrown when an attempt is made to invoke a function with an invalid type of argument. For instance the reduce function / requires either a scalar or a vector on the LHS. Invoking it with an array will trigger a DOMAIN ERROR:
A ← 2 3 4 ⍴ ⍳ 24
B ← 2 2 ⍴ ⍳ 4
B /[2] A
Error
A ← 2 3 4 ⍴ ⍳ 24
B ← 2 2 ⍴ ⍳ 4
B /[2] A
--^
DOMAIN ERROR [LHS must be a vector or a scalar: It has a shape of [2,2] ] on line 3 at character 3
INDEX ERROR
Invalid Axis
Trying to specify an Axis that is out of bounds will trigger an INDEX ERROR.
A ← 2 3 4 ⍴ 1 2 3 4 5 6
2 /[6] A
Gives
Error
A ← 2 3 4 ⍴ 1 2 3 4 5 6
2 /[6] A
--^
INDEX ERROR [Invalid Axis: 6 ] on line 2 at character 3
LENGTH ERROR
Mismatched Shape Errors
The error LENGTH ERROR is a runtime error that is thrown when an operation is attempted on an array that has the wrong shape. The message you get will depend on if the vector being processes is eager or lazy.
1 2 3 + 4 5
An eager vector will be tested before invoking the dyadic function and give this error message:
Error
1 2 3 + 4 5
^
LENGTH ERROR [dimensions mismatch in dyadic [\"+\"]: LHS dimensions \"3\" - RHS dimensions \"2\" ] on line 1 at character 1
A lazy vector doesn’t know it its own length and is typically passed in from Erlang or Elixir. If this expression were evaluated where both the LHS and the RHS were lazy the error message would emerge from the bowels of the dyadic function slightly differently:
Error
1 2 3 + 4 5
^
LENGTH ERROR [dimensions mismatch in dyadic [\"+\"]: ran out of matches after 2 elements ] on line 1 at character 1
Axis Operations
Axis function expect an axis that matches to the shape being operated on and will throw a RANK ERROR is that is not the case:
C ← 2 3 4 ⍴ ⍳24
⍴ ,[3 4] C
Will give:
Error
C ← 2 3 4 ⍴ ⍳24
⍴ ,[3 4] C
--^
RANK ERROR [Invalid Axis: [3,4] ] on line 2 at character 3
This is true for float axis specifications also:
C ← 2 3 4 ⍴ ⍳24
⍴ ,[4.5] C
Will give:
Error
C ← 2 3 4 ⍴ ⍳24
⍴ ,[4.5] C
--^
RANK ERROR [Invalid Axis: 4.5 ] on line 2 at character 3
RANK ERROR
Rank Errors
If you try and invoke an operator with operands of the wrong rank you will get an error. For example the dyadic reduce operator \ requires the left hand operand to be of one rank lower than the right. If the RHS is a scalar then this operation is invalid dyadically.
1 +/ 1
Resulting in:
Error
1 +/ 1
-----^
RANK ERROR [RHS must be an array: It is a scalar ] on line 1 at character 6
SYNTAX ERROR
Variable Name Errors
If you try and use an invalid character in a Variable declaration you will get an error. Invalid characters are whitespace, any of the APL/Pometo unicode symbols and the normal punctuation you find on your keyboard with the exception of _ and -.
In concordance with normal Erlang practice variables in Pometo start with a capital Latin letter ie A-Z.
MyVar≠99 ← 1 2 3
Error
MyVar≠99 ← 1 2 3
---------^
SYNTAX ERROR [syntax error before: ← ] on line 1 at character 10
MyVar~99 ← 1 2 3
Error
MyVar~99 ← 1 2 3
---------^
SYNTAX ERROR [syntax error before: ← ] on line 1 at character 10
myvar ← 1 2 3
Error
myvar ← 1 2 3
^
SYNTAX ERROR [syntax error before: m ] on line 1 at character 1
VARIABLE NOT DEFINED
Undefined Variable Errors
You can’t invoke a variable before it is defined.
A ← 4 5 6 ⋄ B ← 6 7 ¯8 ⍝ including comments
D + C
will give the following error:
Error
D + C
----^
VARIABLE NOT DEFINED [C: variable is not defined ] on line 2 at character 5
Error
D + C
^
VARIABLE NOT DEFINED [D: variable is not defined ] on line 2 at character 1
VARIABLE REASSIGNED
Variable Reassigment Errors
Like in Erlang variables in Pometo are immutable once you have run A ← 1 2 3 then A has the value 1 2 3 as long as it remains in scope.
Redefining a variable will give you a VARIABLE REASSIGNED error.
A ← 4 5 6 ⋄ A ← 6 7 ¯8
will give the following error:
Error
A ← 4 5 6 ⋄ A ← 6 7 ¯8
------------^
VARIABLE REASSIGNED [A: was previously assigned on line 1 at char 1 ] on line 1 at character 13